Remove obsolete Ceph tags

Remove obsolete Ceph tags

  This patch removes the logic to use an specific tag for
  Ceph containers. We will use whatever docker image TripleO
  upstream uses. For aarch64, an ansible task will replace
  the tag to pull the proper container image.

  This patch also refactors the preparation of the local
  registry. In Queens, there is no need to execute twice
  the overcloud container image prepare command.

JIRA: APEX-622

Change-Id: I947d931609e58505675bb460a59d08c1d10d1d0b
Signed-off-by: Ricardo Noriega <rnoriega@redhat.com>