Implement server routing (stopped working with Neo4j Aura)

[jgaskins]

I think the new server routing for Neo4j clusters has botched the cluster connection management in Neo4j::Cluster on Neo4j Aura. I'd heard about the new server routing, but assumed everything would continue working. Unfortunately, all the DBs in my my Neo4j Aura cluster point at the same IP address (presumably an L4 load balancer), so connecting requires relying on server routing outside the client's control.