[WIP][DO_NOT_MERGE] add an upstream image field to builds

are you referring to the RepositoryName field?  i'm maintaining consistency w/ deployments:
https://github.com/openshift/origin/blob/master/pkg/deploy/api/types.go#L153

however the entire field is going to change to be an ObjectRef shortly so i'll consider a name change to just "repository" at that point.