LU-9966 tests: sanity-411 check LBUG direct

LU-9966 tests: sanity-411 check LBUG direct

The sanity test_411 intends to catch LBUG while IO
under memory pressure. It assumes that 'dd' would
fail because memory alloction failure. But it is
not ture since RHEL7 has some problem in memory
accounting. So we can ignore the 'dd' status.

Test-Parameters: trivial

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: Ie9af0fe68c85a9e2af4da6b49d0a697d00f3761b
Reviewed-on: https://review.whamcloud.com/32293
Tested-by: Jenkins
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>