overlay: test encode/decode overlay file handles with renames

overlay: test encode/decode overlay file handles with renames

- Check decode/read of file handles after rename of parent
- Check decode/read of file handles after rename of grandparent
- Check decode/read of file handles after move to new parent
- Check encode/decode/read of file handles in non-upper overlay

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.

This test covers only encode/decode of file handles for overlayfs
configuration of all layers on the same base fs.

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