This avoids a potential circular dependency where the registry is the
source of its own image.
Also fixes up the image building documentation about the default value
of kolla_docker_registry.
Change-Id: Ia30173abf185329098ace621baf0ad1be75c0b74
Story: 2004820
Task: 29345
This commit changes the docker-registry playbook to deploy a Docker
Registry on hosts in the docker-registry group, rather than being
harcoded to deploy on the first controller.
The default location is changed to deploy on the seed as it appears to
be a good location for most deployments.
UpgradeImpact: The Docker Registry is now deployed on the seed by
default.
Change-Id: I87d02bd9556afb795c8783ed78e797fdd31fe8ca
Story: 2004820
Task: 28986