Refactor: scheduler: add bundle meta-attribute in primitive method

Previously, pcmk_graph_producer.c:add_action_attributes() called the resource's
add_graph_meta() method to add relevant meta-attributes to the action XML, but
then it explicitly added the "external-ip" meta-attribute itself.

Since that is only set on bundle replica children, which must be primitives,
it makes more sense to do that in the primitive add_graph_meta() method.