librbd: deep-copy should update object-map before writing to object

librbd: deep-copy should update object-map before writing to object

For the original use-case of RBD mirroring it was (maybe) more
acceptable to write to the object before updating the object map
because an interrupted sync will be retried. However, when using
the deep-copy object copy state machine as part of copyup, it's
more likely that the object-map has the potential to become
out-of-sync with reality if it's updated after the object is
written.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit e782b85bfda8ae6487c637af0059ab94fba332d6)

Conflicts:
	src/librbd/deep_copy/ObjectCopyRequest.cc: trivial resolution
	src/test/librbd/deep_copy/test_mock_ObjectCopyRequest.cc: trivial resolution