LU-6540 test: fix no %s specifier for the file

LU-6540 test: fix no %s specifier for the file

The %m prints strerror(errno), but there is no %s specifier for the file.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: Id9a8f486521b94e98986140fa374c40e08a00dac
Reviewed-on: http://review.whamcloud.com/14815
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>