rbd-mirror: configure pool and peer

rbd-mirror: configure pool and peer

The rbd mirror configuration was only available for non containerized
deployment and was also imcomplete.
We now enable the mirroring on the pool and add the remote peer in both
scenarios.

The default mirroring mode is set to 'pool' but can be configured via
the ceph_rbd_mirror_mode variable.

This commit also fixes an issue on the rbd mirror command if the ceph
cluster name isn't using the default value (ceph) due to a missing
--cluster parameter to the command.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1665877
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>