quota: clear speculative delalloc when checking quota usage

quota: clear speculative delalloc when checking quota usage

Occasionally speculative preallocation kicks in when writing files
to a filesystem under test.  These preallocations consume quota and
/usually/ aren't around after we drop_caches, but there's nothing to
guarantee that they actually have, so the quota reports will be
different before and after the fs remount, causing sporadic test
failures in generic/{23[123],270}.

We now have xfs_spaceman which can instruct XFS to forcibly remove
the speculative preallocations.  This fixes the sporadic failures,
at least for XFS.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>