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/image/RemoveRequest.cc: trivial resolution
	src/test/rbd_mirror/image_deleter/test_mock_SnapshotPurgeRequest.cc: DNE
	src/tools/rbd_mirror/image_deleter/SnapshotPurgeRequest.cc: DNE
	src/tools/rbd_mirror/image_deleter/SnapshotPurgeRequest.h: DNE
	src/librbd/DeepCopyRequest.cc: (see below)
	src/librbd/deep_copy/ObjectCopyRequest.cc: (see below)
	src/librbd/deep_copy/ObjectCopyRequest.h: (see below)
	src/librbd/deep_copy/SetHeadRequest.cc: (see below)
	src/librbd/deep_copy/SetHeadRequest.h: (see below)
	src/librbd/deep_copy/SnapshotCopyRequest.cc: (see below)
	src/librbd/deep_copy/SnapshotCopyRequest.h: (see below)
	src/librbd/deep_copy/SnapshotCreateRequest.cc: (see below)
	src/librbd/deep_copy/SnapshotCreateRequest.h: (see below)
	src/test/librbd/deep_copy/test_mock_ObjectCopyRequest.cc: (see below)
	src/test/librbd/deep_copy/test_mock_SetHeadRequest.cc: (see below)
	src/test/librbd/deep_copy/test_mock_SnapshotCopyRequest.cc: (see below)
	src/test/librbd/deep_copy/test_mock_SnapshotCreateRequest.cc: (see below)
	src/test/librbd/test_mock_DeepCopyRequest.cc
- deep-copy related files were originally derived from rbd-mirror
  equivalents. Similar modifications where made to the associated
  rbd-mirror files.