LU-4351 tests: skip loop test in SLES11 clients

LU-4351 tests: skip loop test in SLES11 clients

Avoid known failure in test 54c due to SLES specific
incompatible implementation flaw in kernel loop devices.

Lustre-commit: f5683b151be0e8ba0d41e85a8f99850c7d00e55c
Lustre-change: http://review.whamcloud.com/9955

Test-Parameters: clientdistro=sles11sp3 testlist=sanity
Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Change-Id: If39aa85e8c1f468df532aa93610d3eb7cd8d32f5
Reviewed-on: http://review.whamcloud.com/10085
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>