LU-15429 tests: mount_mds_client() fix

LU-15429 tests: mount_mds_client() fix

mount/umount client is to be executed on active facet/host,
not on mds1_HOST. Without this fix test_140a() fails on
failover setup:
  CMD: lm0101 umount /mnt/lustre2 2>&1
  CMD: lm0102 rmdir /mnt/lustre2
  lm0102: rmdir: failed to remove '/mnt/lustre2':
                 No such file or directory
  test_140a: FAIL: no clients with recovery disabled

To reproduce the failure just run:
  ONLY="107 140a" sh recovery-small.sh
on failover setup where mds1_HOST != mds1failover_HOST.

Fixes: 8bd04b4e57 ("LU-12722 target: disable recovery for local clients")
Test-Parameters: trivial env=ONLY="140a 140b" testlist=recovery-small
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-10669
Reviewed-by: Vladimir Saveliev <vlaidimir.saveliev@hpe.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: Ifbdedfda840e8421fa8a969f73131ca23982a28b
Reviewed-on: https://review.whamcloud.com/46043
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>