LU-4016 tests: use user and group names in metadata-updates

LU-4016 tests: use user and group names in metadata-updates

pdsh eats %u passed to stat executed on remote nodes.  Avoid this
problem by using the user and group names instead of numerical
identifiers in metadata-updates ownership checks.

Test-Parameters: testlist=metadata-updates
Signed-off-by: James Nunez <james.a.nunez@intel.com>
Signed-off-by: Stephen Champion <schamp@sgi.com>
Change-Id: Id0a283d58873bb64772f28cbc28c5a6abad9a48e
Reviewed-on: http://review.whamcloud.com/8052
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>