overlay: test overlay file handles of lower dir with non-indexed ancestor

overlay: test overlay file handles of lower dir with non-indexed ancestor

Overlayfs with nfs_export enabled, indexes all directories on copy
up.  Directory index is requires for decoding lower directory file
handles in case ancestors have been renamed.

When enabling nfs_export on an overlay that already has non-indexed
merge dirs, the possibility of non-indexed ancestor rename requires
special handling when encoding lower directory file handles.

- Check encode/decode/read file handles of non-indexed merge dir
- Check encode/decode/read file handles of dir with non-indexed parent
- Check encode/decode/read file handles of dir with non-indexed grandparent
- Check decode/read of file handles after rename of non-indexed merge dir
- Check decode/read of file handles after rename of non-indexed parent
- Check decode/read of file handles after rename of non-indexed grandparent

This test requires and enables overlayfs NFS export support and
merge dir rename support (redirect_dir).
NFS export support depends on and requires overlayfs index feature.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>