librbd: use the correct error code when the exclusive lock isn't locked

librbd: use the correct error code when the exclusive lock isn't locked

If the client is currently blacklisted, use -EBLACKLISTED, otherwise
use -EROFS.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit e8eee15518facf562adf1aaba02d3a9523cdd2c3)

Conflicts:
	src/librbd/ExclusiveLock.cc: trivial resolution
	src/librbd/Operations.cc: trivial resolution
	src/librbd/deep_copy/ObjectCopyRequest.cc: trivial resolution
	src/librbd/deep_copy/SetHeadRequest.cc: trivial resolution
	src/librbd/deep_copy/SnapshotCopyRequest.cc: trivial resolution
	src/librbd/deep_copy/SnapshotCreateRequest.cc: trivial resolution