xfs/422: use new -f option to xfs_io repair

Since we changed online scrub to require the FREEZE_OK flag, we have to
tell xfs_io that we want that in order to get any rmapbt repairs at all.
Make sure we thaw the fs at cleanup time so that we can unmount it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>