LU-16252 tests: test_129() fix for not combined_mgs_mds

LU-16252 tests: test_129() fix for not combined_mgs_mds

To reproduce the failure, just run test_129 on not
combined_mgs_mds setup:
  ONLY=129 sh conf-sanity.sh
    Start of /dev/vdb on ost1 failed 110
    conf-sanity test_129: @@@@@@ FAIL: start ost1 failed

Fixes: cefabee525 ("LU-15112 mgc: do not ignore target registration failure")
Test-Parameters: trivial testlist=conf-sanity env=ONLY=129 combinedmdsmgs=false
Test-Parameters: testlist=conf-sanity env=ONLY=129 combinedmdsmgs=true
HPE-bug-id: LUS-10708
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Change-Id: If8317feb40345d057a0e38dfb4ff95448953f6ff
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48918
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alexander <alexander.boyko@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>