LU-6913 test: fix conf-sanity test_30b defect

LU-6913 test: fix conf-sanity test_30b defect

test_30b does not take into account a failover nid set
before test started, which leads test always fails
on the setup with $ost1failover_HOST != $ost1_HOST;
Patch fixes this defect.

Signed-off-by: Elena Gryaznova <elena.gryaznova@seagate.com>
Seagate-bug-id: MRP-2749
Reviewed-by: Andriy Skulysh <andriy.skulysh@seagate.com>
Change-Id: I2f7f163b84e4203ffa0ab12bc18b9d7ac535ec37
Reviewed-on: http://review.whamcloud.com/15772
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>