LU-2789 mdt: ensure constant striping during chown()

LU-2789 mdt: ensure constant striping during chown()

Prevent concurrent setstripe and chown() operations on a file by
acquiring mot_lov_mutex in mdt_attr_set(). This is needed to maintain
consistency between the ownership of files and their sub-objects and
to ensure that attribute changes on sub-objects are properly declared.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I75fe3476a284dccde5312a5c3f79b3698610ef25
Reviewed-on: http://review.whamcloud.com/6070
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>