LU-4725 mdt: child-parent lock ordering in rename

LU-4725 mdt: child-parent lock ordering in rename

change rename so that it always has parent-child lock ordering,
otherwise it may deadlock with other operations.

Lustre-commit: 4e308ef74f271ec7e19917e3c0f88586537582c3
Lustre-change: http://review.whamcloud.com/9538/

LU-4725 obd: lu_object_find_at hung

lu_object_find_at hungs if called 2 times and object is removed
in between. It makes mdt_rename_sanity not workable for rename.
Change mdt_rename_sanity to work on existing object.

Lustre-commit: b7c72ec1ddeda2cf94ea151f974d3f94e3a7d1ed
Lustre-change: http://review.whamcloud.com/10484/

Test-Parameters: alwaysuploadlogs \
envdefinitions=SLOW=yes,ENABLE_QUOTA=yes,ONLY=54 \
ossjob=lustre-b2_4 mdsjob=lustre-b2_4 ossbuildno=73 mdsbuildno=73 \
testlist=sanityn

Signed-off-by: Rahul Deshmukh <rahul_deshmukh@xyratex.com>
Signed-off-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Change-Id: Ic9ce52bfcd8788834347fba155cc8c6be674dcd8
Reviewed-on: http://review.whamcloud.com/11615
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>