xfs_scrub: check directory connectivity

xfs_scrub: check directory connectivity

Opening directories by file handle will cause the kernel to perform
parent lookups all the way to the root directory.  Take advantage of
this to ensure that directories actually connect to the root.  Some
day we'll have parent pointers and can make this more comprehensive.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>