GitLab

* 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"