update: add containerized deployment upgrade support (L->N)

update: add containerized deployment upgrade support (L->N)

Add a couple of fixes to allow containerized deployments upgrade support
to upgrade from luminous/mimic to nautilus.

- pass CEPH_CONTAINER_IMAGE and CEPH_CONTAINER_BINARY environment
variable to the ceph_key module,
- fix the docker exec command in 'waiting for the containerized monitor
to join the quorum' task according to the `delegate_to` parameter,
- override `docker_exec_cmd` in `ceph-facts` with `mon_host` when
rolling_update is `True`,
- do not run unnecessarily `create_mds_filesystems.yml` when performing an
upgrade.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>