mds: use "open-by-ino" helper to handle LOOKUPINO request

Fixes #3541
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: kill Server::handle_client_lookup_hash()

Server::handle_client_lookup_ino() is more simple and robust. Use it
to handle both LOOKUPHASH and LOOKUINO requests.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: rev protocol

Commit 18b9e63b4df643e1f2fb8f17416089e5d970bf60 changed the OTW lock
encoding.

Signed-off-by: Sage Weil <sage@inktank.com>