rbd-mirror: early detect if the mirroring instance match global group id

rbd-mirror: early detect if the mirroring instance match global group id

In a case where previous primary cluster is still alive,

-> Force promote site-b while site-a is still alive
-> Disable group on site-b
-> Re-enable group on site-b, while site-a is still alive

the group is getting removed. To avoid any such cases, better to makesure
the instance match with local group id, before taking any actions.

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>