LU-13599 mdt: add test for rs_lock limit exceeding

LU-13599 mdt: add test for rs_lock limit exceeding

The check conditions in mdt_link_parents_lock() considers there
can be total 6 local locks but in fact when object has hard links
then it is regular file and it may have maximum 5 local locks.

Patch updates that check conditions for rs_locks as small
improvement and ports test for rs_locks limit from 2.12.

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I98cca84825ce5789094fbceb5d1f7975410d134b
Reviewed-on: https://review.whamcloud.com/39194
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Stephane Thiell <sthiell@stanford.edu>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>