Adds build and publishing jobs for CentOS 8 images:
- kolla-build-centos8-binary
- kolla-build-centos8-source
- kolla-publish-centos8-binary
- kolla-publish-centos8-source
The 'base' image has been added to the list of unbuildable images for
CentOS 8 (now separate from the list for CentOS 7). This means that no
images will be built - the jobs should essentially be a 'noop'.
Change-Id: Ie9a0109bd4eef337358d714e4b5088b8e3de2f23
Partially-Implements: blueprint centos-rhel-8
b060623b90