The current `openstack tripleo container image build` defaults result
in a failed build for the following reasons:
- The base image is ubi8 (rhel)
- The default --distro is centos
- tcib_release is a mandatory variable but is unset, resulting in a
build failure
This change does the following:
- default --base is now centos:stream9
- new argument --release defaults to '9', which sets tcib_release
This results in built cs9 container images without requiring any
--base or --tcib-extras arguments.
Change-Id: I69346aa10d734580ba66e0dd571a27e46e123fe8
54898e34f1