LU-1601 ldlm: Fix flock detection for different mounts

LU-1601 ldlm: Fix flock detection for different mounts

Deadlock can happen when 2 processes take concurrent locks
on files situated in different mountpoints.

Modify flock detection algorithm to distinguish process by
pair PID+NID instead of PID+export.
It is done by searching for a blocking owner in all OBD's
exports with the same NID.

Xyratex-bug-id: MRP-449
Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Reviewed-by: Bruce Korb <bruce_korb@xyratex.com>
Change-Id: Ib2969df9b9733af4025e1905caf2378af72c6f18
Reviewed-on: http://review.whamcloud.com/3276
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>