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): 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
style(controller): fix flake8
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.
feat(controller): add PUBLIC_INDEX_URL setting

This setting is useful for id index.docker.io ever changes.
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.
fix(client): remove latest tag appending

Registry repository imports does not like tags.
fix(controller): add worker soft timeout

`docker build` can take a while, which times out the builders. Adding
a larger timeout gives us some more leeway.
Revert "fix(controller): add worker soft timeout"

This reverts commit f3a87567c209a2eda5e1ba8a5104cfce35ae6431.