This commit adds support for CoreDNS through its etcd middleware.
Because the middleware is backward compatible with SkyDNS this
commit adds support for SkyDNS as well. In fact, new provider
is available under two names in CLI (coredns and skydns).

All interactions with middleware happen through etcd cluster,
whose location (URIs) is specified via --etcd CLI parameter
by default http://localhost:2379).

The provider translates CoreDNS/DkyDNS SRV records to
A/CNAME + optional TXT endpoints, when reading from etcd and
combines A/CNAME with TXT endpoints back into single SRV record
when writing it back.

Also adds github.com/coreos/etcd package to glide.yaml and vendor folder
because it is used by the provider

- Add `--inmemory-zone flag`
- Implement `InMemoryZoneInit` function to setup initial zones for
  inmemory provider
- Make "" the default zone for the inmemory provider instead of
  nil/none when no initial zones are specified
- Update config/flag parsing tests to accept new flag

* Initial commit of Infoblox provider

* address @ideahitme's observations

* fail at addressing @szuecs comments

* fix(infoblox): avoid shadowing err variable

* fix flag descriptions

* default ssl verify to true. thanks @szuecs

* chore(infoblox): bump minium required version

This should ideally be a minor bump but let's do that when we have v0.5

* Adds Dnsimple as a provider

* chore(vendor): remove vendor for smaller diff

* fix(config): make dnsimple selectable via flags

* Fix delete and update

* Dnsimple testify mock tests

* remove leaked file

* Move and simplify mock functions

* chore: use lowercase for logrus repository

* chore: update dependencies using glide

* chore: vendor dnsimple-go package

* ref: isolate suitable type in source package

* add support for DNSimple, thx @jose5918 :D

* chore: use lowercase for logrus repository

* chore: update dependencies using glide

* Add a new --cloudflare-proxied flag to toggle Cloudflare proxy feature

* Change flag description

* ClusterIP service support

- First pass at addresssing #187 by allowing services with type ClusterIP to be directly supported

* Getting existing tests to pass

* Adjusting formatting for gofmt/govet

* Adding in guard logic around publishing of ClusterIP sources

* Addressing PR feedback

* Adding in CHANGELOG entry

* Adding in Headless service test

* ref(sources): refactor source registration and lookup to be lazy.

* fix(fake): don't make changes to passed in config values

* rework without init, tests are missing

* make client provider public

* fix all tests

* change parameter list order, minor improvements

* clientprovider -> clientgenerator, switch naming for interface/struct

* Support for multiple domains within --domain-filter

The parameter accepts a comma separated list of domains with or without trailing dot. Example: --domain-filter="example.org, company.test.,staging.com". Closes #247 and #229

* Add boilerplate header

* Add documentation for methods and structs

* use StringsVar for the domain-filter flag

* go fmt

* Remove camel case from tests

* Revert changes in README.md

* Move DomainFilter to provider package

* Make a new slice and copy elements to it

* Update CHANGELOG.md

* docs: change minor spelling mistake

* CloudFlare Provider

* updating glide

* gofmt cloudflare_test.go

* Unset envs to test NewCloudFlareProvider

* More tests

* fix(cloudflare): fix compiler errors resulting from merge

* Typo

* Undo vendor changes

* decrease api calls, fix some nits

* Cloudflare iteration (#2)

* reduce the number of API calls

* match by type and name for record id

* improve coverage and fix the bug with suitable zone

* tests failed due to wrong formatting

* add cloudflare integration to the main

* vendor cloudflare deps

* fix cloudflare zone detection + tests

* fix conflicting test function names

* Initial Digital Ocean as a new provider

* chore: vendor dependencies

* Remove zone parameter from ApplyChanges and Records

* fix(digitalocean): fix correct imports, unshadow a variable

* fix(digitalocean): respect domain-filter if provided

* add changes to digital ocean provider from PR review (#3)

* fix tests and bugs in find suitable zones for digital ocean (#5)

* tests failed due to wrong formatting

* add digitalocean integration to the main and more tests

* fix suitable zone for digital ocean

* fix: Load all known Kubernetes Auth Plugins

* chore: vendor CoreOS' oidc library

* vendor Azure Go SDK (#210)

* vendor the Azure Go SDK and dependencies

* add initial Azure DNS provider implementation (#210)

* add 'azure' value to 'provider' command line option
* add 'azure-config-file' command line option
* add 'azure-resource-group' command line option
* implement initial Azure DNS provider

note: azure provider is not yet fully implemented (does not query for existing
records).

tests and documentation are forthcoming.

* add a tutorial for the Azure provider (#210)

* add tutorial for using ExternalDNS with Azure DNS

* finish implementation of Azure DNS provider (#210)

* implement the Records method for the Azure DNS provider

* refactor Azure API interface for future tests (#210)

* make Azure provider use an interface for future unit tests

* add unit tests for the Azure provider (#210)

* test retrieving Azure DNS records.
* test updating and deleting Azure DNS records.
* test dry run for the Azure provider (i.e. noop).

* Expose inmemory provider to cli

So we can test `--source fake` without needing to touch AWS/Google.

* Add FakeSource

`external-dns --provider inmemory --source fake --dry-run --once`

OR

`external-dns --provider aws --source fake --fqdn-template <hostname suffix> --dry-run --once`

NB: `--fqdn-template` because otherwise we'll default to creating, e.g.,
`abcd.example.com`, which `--provider aws` filters out because you
likely don't have a Zone for `example.com.`  Could also be resolved by
removing the need to use a real provider; the inmemory provider,
perhaps, though it's not entirely hooked up.

Closes kubernetes-incubator/external-dns#22

* Style feedback from Travis CI

* Improve optionality of kubernetes client

* ref(sources): refactor source registration and lookup to be lazy.

* Revert "ref: refactor source registration/lookup to be lazily initialized"

* chore: add instrumented HTTP client library

* feat: add client-side metrics to outgoing HTTP clients

* feat: add and use a deduplicating source

* chore: add log entry when endpoint was deduplicated

* feat(config): change defaults, switch flag processing to kingpin

* chore: vendor kingpin as a dependency

* feat(config): auto-detect cluster config from the environment

* chore: clean up definition of flags

* chore: sanitize flags even further

* chore: update changelog with latest flags changes

* fix(aws): fix messed up test name

* minor improvements to logging

* chore(*): change log.Infoln to log.Info

* fix: fix incorrect example code

* feat(google): auto-detect and multiple zone support

* chore: run gofmt with the simplified command

* fix: pass desired domain to google provider

* feat(google): correctly auto-detect records for sub-zones

* chore: update changelog with support for multiple zones in google

* fix(google): don't append traling dot to TXT records

* ref(provider): extract hostname sanitization to general provider

* add --fqdn-template

* add missing ,

* gofmt

* no endpoint creation on empty fqdntemplate

* improve test coverage

* gofmt simple on service_test.go and ingress_test.go

* import package order changed

* gofmt

* refactor to generate template in the source init

* refactor for err handling

* fix service tests

* fix wrong check, check for priorities, mate > template

* fix tests, check for controller annotation in the right place

* add to changelog

* add flag description, improve testing, reorganize imports

* review changes: log the error, use text/template, change func interface

* feat(aws): support multiple hosted zones and automatic lookup

* chore: run gofmt with the simplified command

* fix(aws): add missing method from google provider

* fix: remove superflous parameter from google provider

* feat: make domain configurable via flag

* fix(aws): remove unused constant

* fix(aws): don't log actions that were filtered out

* feat(aws): detect best possible zone to put dns entries in

* fix(aws): log error instead of failing if a change batch fails

* chore: update changelog with support for multiple zones

* feat(plan): allow plans to be parameterized via policies

* fix(controller): set a policy in the controller tests

* chore: allow go tip to fail

* chore: update changelog to include policies

* fix(plan): store a pointer to changes

* fix(controller): don't get address of a pointer

* kickoff txt registry

* fix inmemory dns provider to include recordtype info for validation

* Merge master

* fix ununsed variable in inmemory provider

* add tests for records

* add test for no prefix name formatter

* implement apply changes with tests

* add flag to enable txt registry

* add txt registry to main

* improve sort testing

* filter out non-owned records

* NewEndpoint(...) requires record type

* use newendpoint in aws_test, fix tests

* change suitable type implementation

* fix the test for compatibility component

* change inmemory provider to include recordtype and use suitable type

* fix comments, CNAME should target hostname

* name mapper do not use pointer on struct

* txt prefix - just concatenate, remove spew, fix txt record label

* allow TXT records as result from dns provider

* add changelog

* fix tests

* TXT records need to be enclosed in double quotes

* define registry interface

* init in-memory registry

* remove ununsed variable, added comments

* add inmemory registry tests

* introduce DNSRecord struct

* use noop registry

* remove zone from registry fields

* replace provider with registry in controller

* move noop registry interface check to test

* remove ownerid from noop registry

* fix: remove dangling empty line

* return provider records directly with noop

* adjust according to pr review

* fix noop tests

* feat: expose basic go metrics via prometheus

* chore: vendor dependencies

* feat(metrics): combine healthz and metrics into single endpoint

* ref(metrics): rename metrics port to address

* docs(metrics): update changelog to include metrics feature

* ref(metrics): consistently rename port to address

* fix(dnsprovider): do not always initialize each DNS provider

* fix(dnsprovider): fix unnecessary error return value

* ref(dnsprovider): drop the store and use a simple switch for lookup

* ref(source): use constructor methods to create sources

* fix: import and use missing package

* fix(source): fix merge conflict with master branch