LU-9966 test: add a skip test to test_411

LU-9966 test: add a skip test to test_411

Since recently added test_411 needs a /sys nntry that doesn't exist
in sles12 extend the existing skip logic to skip the test in the case
of the entry being missing.

Test-Parameters: trivial clientdistro=sles12sp2 \
  testgroup=review-ldiskfs

Change-Id: I1f1bf05affdc1cec9957624506dac65e59f5b4ad
Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-on: https://review.whamcloud.com/28974
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>