LU-3624 utils: fix lctl test_mkdir for use in mds-survey

LU-3624 utils: fix lctl test_mkdir for use in mds-survey

The mds-survey script uses the 'lctl test_mkdir' command to create
directories for metadata tests. This currently raises the following
error message:
"...stre-2.4.0/lustre/include/lustre/lustre_idl.h:683:ostid_set_id())
Bad 18446744073709551615 to set 0:0"

This patch fixes the jt_obd_md_common() routine to avoid this error
to be generated.

Signed-off-by: Gregoire Pichon <gregoire.pichon@bull.net>
Change-Id: Idccc13166d6160bfb5f9ac6a79911cc27bfe77a2
Reviewed-on: http://review.whamcloud.com/7101
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Bobbie Lind <bobbie.j.lind@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>