fix(controller/registry): strip hostname from repo

The changes to the registry module did not strip the hostname from the
app image. This fixes that by properly parsing the source for the
repository name in the registry and the tag.
Merge pull request #1500 from deis/hotfix-registry-module

fix(controller/registry): strip hostname from repo
fix(controller): Determine registry address during start

Before this change re-deploying apps failed when the registry was
re-scheduled to a different instance in the cluster.

Fixes #1128