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
> This change is only stored in the controller reference and not in the registry.

I'm not sure what you mean by that. They already have a fixed name (the root of the registry, which in dockerland also implies as the `library` org). The controller references this image ID to modify the image on `config:set` or with `releases:rollback` in the controller to create a new release. Because no image on the registry exists as `deis-registry/app_name` the registry module will fail over. I still don't see the need for this change. Could you please elaborate more on why this change is necessary for this PR?