xfs: be compatible with older mkfs.xfs which has no v5 support

xfs: be compatible with older mkfs.xfs which has no v5 support

With the change to CRCs by default, some tests are updated to call mkfs
with "-m crc=0" option directly, and this breaks testings on older
distros where mkfs.xfs doesn't have crc support.

Introduce a new variable to tell if mkfs.xfs supports v5 xfs and do
tweaks in _scratch_mkfs_xfs_opts() based on it.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>