LU-2284 quota: debug patch for test_7d

LU-2284 quota: debug patch for test_7d

Try to collect D_TRACE & D_QUOTA log to see why the setquota failed
with -EINVAL.

This patch improve the test script a bit: fail the test when setquota
failed.

Test-Parameters: testlist=sanity-quota
Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: Ic866dcefcb174bd0128e63f5777824608db52962
Reviewed-on: http://review.whamcloud.com/4510
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>