MRP-904 tests: sanityn 33a: wrong print_jbd_stat() procfile

The procfile name used by print_jbd_stat() is incorrect, test_33a
does not fail if "info" file is not found.
The fix is ported from LU-2829.
Error is added if test failed to get jbd stat.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Signed-off-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Change-Id: I210b775c2df47380a899bfdc07c0b161cc6b8a21
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/407
Tested-by: Jenkins
Reviewed-by: Vladimir Saveliev <vladimir_saveliev@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>