rbd-mirror: add mirror status removal on ImageReplayer shutdown

rbd-mirror: add mirror status removal on ImageReplayer shutdown

In a scenario where you have rbd-mirror daemons on both clusters. The
rbd-mirror daemon on the primary site will not properly cleanup his
status on image removal.

This commit add a path for direct removal at the shut_down of the
ImageReplayer to properly cleanup the metadata.

Signed-off-by: Arthur Outhenin-Chalandre <arthur.outhenin-chalandre@cern.ch>
(cherry picked from commit a538c5d279c90397d375668baddd65776d2462b0)

Conflicts:
        src/test/rbd_mirror/test_mock_MirrorStatusUpdater.cc
- Trivial conflict resolution; io_ctx exec has 1 less argument