fix(controller): remove docker engine

The intention of the docker engine was such that we could use it to pull in an image
from a registry and push it to our own. Now that we have registry transfers, this
is no longer required.
fix(controller): use private module

Since docker-in-docker is not installed on the controller any more, let's revert
back to the private module.
fix(client): add "but first, coffee" string back
fix(client): use present tense when rolling back
style(controller): add newline
fix(controller): use /bin/sh as entrypoint for run
fix(controller): update release process
fix(controller): update mock registry
fix(registry): fix upstream changes

Some things changed with the version bump like how the docker registry process is
started and where dependencies are installed from.
fix(controller): import image from remote registry

This change allows us to import an image from a remote repository,
thanks to a new feature implemented in
https://github.com/deis/docker-registry/compare/repository-import.

Though the infrastructure in place allows us to import an image from the public index,
the endpoints are closed-source and therefore are not implmented in the upstream
repository-import branch.
fix(controller): add back REGISTRY_URL
fix(controller): clean up publish_release params

Publishing a release should only know about a source, a dictionary of
configuration, and a target.
refactor(controller): clean up Release.new
refactor(controller): remove urlparse logic

The logic has been moved over to the registry, so it's not needed any more.
style(controller): fix flake8
test(controller): mock import_repository task
fix(builder): revert target_image

When target_image was POST'd to the controller through /api/hooks/build,
the tag was not originally sent. Reverting the behaviour so `git push deis master` works
again.
fix(controller): correct image name parsing
fix(controller): build image from source_tag

'sha' is just metadata. it is not used as a tag on the registry.

The release ledger is append-only, which means that the latest image should be
used by default, with an optional source tag for rollbacks.
docs(using_deis): add docs for `deis build`