librbd: always refresh after creating snapshot in CreatePrimaryRequest

librbd: always refresh after creating snapshot in CreatePrimaryRequest

Up until now this was conditioned on whether the caller expressed
interest in the ID of the created snapshot and happened to work only
because CreatePrimaryRequest wasn't actually consulting any mirror
snapshot metadata.  This has just changed with unlink_peer() needing to
see an up-to-date complete flag which is set in SetImageStateRequest
following the write out of image state object(s).

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>