rbd-mirror: prevent image deletion if remote image is not primary

rbd-mirror: prevent image deletion if remote image is not primary

A resync on a mirrored image may incorrectly results in the local
image being deleted even when the remote image is no longer primary.
This issue can occur under the following conditions:
* if  resync is requested on the secondary before the remote image has
  been fully demoted
* if the demotion of the primary image is not mirrored
  due to the rbd-mirror daemon being offline.

This can be fixed by ensuring that image deletion during a resync is
only allowed when the remote image is confirmed to be primary.

This commit fixes the issue only for snapshot based mirroring mode

Fixes: https://tracker.ceph.com/issues/70948
Signed-off-by: VinayBhaskar-V <vvarada@redhat.com>