xfs/021: filter v5 filesystem metadata

The xfs_db output is different for v5 filesystem metadata, and so
the test fails due to golden image mismatches rather than an actual
test failure. Improve the filter to hide the differences between the
metadata format outputs.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>