LU-6713 lmv: lock necessary part of lmv_add_target

LU-6713 lmv: lock necessary part of lmv_add_target

Release lmv_init_mutex once the new target is added
into lmv_tgt_desc, so lmv_obd_connect will not be
serialized.

New target should be allowed to added to fld client
lists, so FLD can always choose new added target to
do the FLD lookup request, and also remove some noise
error messages in this process.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I1aa2e31108f2da672b41e2a5c1c544605328ceea
Reviewed-on: http://review.whamcloud.com/15269
Tested-by: Jenkins
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>