fuzz: randomly fuzz XFS and ext4 filesystems

fuzz: randomly fuzz XFS and ext4 filesystems

Introduce tests for XFS and ext4 which format a filesystem, populate
it, then uses blocktrash and e2fuzz to corrupt the metadata.  The FS
is remounted, modified, and unmounted.  Following that, xfs_repair or
e2fsck are run until it no longer finds errors to correct, after which
the FS is mounted yet again and exercised to see if there are any
errors remaining.

The XFS test requires an xfs_db that can handle blocktrash and v5
filesystems.

The ext4 test requires metadata_csum support in e2fsprogs.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>