Bug #2112646 “Kolla image build regex can fail if no registry us…” : Bugs : kayobe

If neither a podman or docker registry are configured, `kolla_docker_registry` evaluates to an empty string. If you try and build some images using a regex, for example with:

`kayobe overcloud container image build nova`

The result is that all images are built, and `nova` is used as the registry. Eg. this runs

`kolla-build –config-dir /opt/kayobe/etc/kolla –engine docker –registry nova`

The expected behaviour is this runs:

`kolla-build –config-dir /opt/kayobe/etc/kolla –engine docker nova`