Using Private Registry doesn't always force a $PORT to be set

[helgi]

deis/builder#409

The current logic for enforcing $PORT is done in registry:set (on the Controller side in the COnfig model). If a user sets a private registry overall via helm then the Controller does not enforce the $PORT behaviour.

Desired behaviour is for both of them to work like registry:set when it comes to $PORT - This might mean raising inside the Release or App model on a deploy