Update git submodules

Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Merge "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>