LU-4098 lmv: Match MDT where the FID locates first

LU-4098 lmv: Match MDT where the FID locates first

With DNE every object can have two locks in different namespaces:
lookup lock in space of MDT storing direntry and update/open lock
in space of MDT storing inode. In lmv_find_cbdata/lmv_lock_lock,
it should try the MDT that the FID maps to first, since this can
be easily found, and only try others if that fails.

In the error handler of lmv_add_targets, it should check whether
ld_tgt_count is being increased before ld_tgt_count is being -1.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Idf90ff97421102da97febb0aebaff3f702ff5df7
Reviewed-on: http://review.whamcloud.com/8019
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>