librbd/mirror: leave non-primary snapshot images in creating state

librbd/mirror: leave non-primary snapshot images in creating state

The creating state is a special case in rbd-mirror where it will
automatically delete the image since it assumes it's malformed.
A non-primary, snapshot-based mirror image needs to have at least
one non-primary snapshot and the first one is not created until
after replay has started. Now rbd-mirror will update the mirror
image state to the enabled state after creating the first
non-primary snapshot but before attempting the sync.

Fixes: https://tracker.ceph.com/issues/49238
Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit 43f2c208fa3042d93e4810d804ffe28e9ca7af77)