LU-6836 tests: Skip sanity-quota test 4a for ZFS

LU-6836 tests: Skip sanity-quota test 4a for ZFS

sanity-quota test 4a is failing frequently in
review-zfs-part-1 test groups. We are temporarily disabling
this test until a fix is submitted.

Note that LU-6836 is thought to be caused by bad ZFS sync
performance. We should reenable test 4a when ZIL support
is ready (LU-4009).

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I07867458e4365c0b1d31654be08e0fef9092c9eb
Reviewed-on: http://review.whamcloud.com/15679
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>