LU-946 lprocfs: List open files in filesystem

LU-946 lprocfs: List open files in filesystem

Added lprocfs file on MDT to list open files in per-export
directory for mdt.

Test-Parameters: testlist=sanity,sanityn
Signed-off-by: Girish Shilamkar <gshilamkar@ddn.com>
Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: If8f233d95dca4cd4c4044d85bd117a027dabd80e
Reviewed-on: http://review.whamcloud.com/6386
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Swapnil Pimpale <spimpale@ddn.com>