Add tests for triggering the role conflict when a wl_surface is already
a wl_shell_surface and then attempted to be made into a sub-surface, and
vice versa.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Jasper St. Pierre <jstpierre@mecheye.net>
