xfs/187: don't rely on FSCOUNTS for free space data

xfs/187: don't rely on FSCOUNTS for free space data

Currently, this test relies on the XFS_IOC_FSCOUNTS ioctl to return
accurate free space information.  It doesn't.  Convert it to use statfs,
which uses the accurate versions of the percpu counters.  Obviously,
this only becomes a problem when we convert the free rtx count to use
(sloppier) percpu counters instead of the (more precise and previously
buggy) ondisk superblock counts.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>