vfs: stub lchown

We already stub chown and fchown. rpm hits lchown in some package installations.
I haven't looked in detail, but it is very likely that it happens when installing
symlinks.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>