Test the functionality associated with node add :
When consensus is reached on a vote for a node's add, it should be properly added into peer_manager
If create_gossip() is called for a peer which is not yet active or doesn’t exist yet, we return an error.
If handle_response is called before handle_request, we handle normally by returning an InvalidResponse to routing.
If no event contained Observation::Add(us), we return with error immediately and add nothing to our gossip graph.
If the sets are different, we return with error immediately and add nothing to our gossip graph.
Once handle_request was called once, we behave for all intents and purposes the same as any other peer.