modify out to allow optional registry to push to
modify out to allow optional registry to push to

[#92837942]

SillyMoo/docker-image-resource,ggeorgiev/docker-image-resource,concourse/docker-image-resource,concourse/docker-image-resource,ggeorgiev/docker-image-resource,SillyMoo/docker-image-resource,barthy1/docker-image-resource,Pivotal-DataFabric/docker-image-resource,barthy1/docker-image-resource