LU-10680 tests: fix interop for sanity test_160h

LU-10680 tests: fix interop for sanity test_160h

Add a check sanity test_160h whether /sbin/umount.lustre is installed
on the MDS, since this subtest is checking whether the MDS unmount
process has completed, and otherwise fails during interop testing.

Test-Parameters: testlist=sanity env=ONLY=160 serverversion=2.12
Fixes: 31fef6845e8b ("LU-10680 mdd: create gc thread when no current transaction")
Signed-off-by: Xing Huang <hxing@ddn.com>
Change-Id: I6720b9e27a3a92e543ed877453802d23c0eef36d
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53773
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>