Add support for aurora protocol without load balancing

We have several use cases that would be ideal for an aurora mode without load balancing - say aurora-sequential.

We have non-global replicating clusters in various regions that we use sequential connections in case of regional outage. However, these connections cannot be load balanced because of latency between regions. We can tolerate the increased latency in emergency situations but not under normal conditions. However, because we use sequential connections, we cannot handle failover in the same region as well. An aurora without load balancing would be ideal for this.

Also, we have writing standby clusters for a regional outage as well but given the access patterns of this code, we cannot tolerate load balancing for writes either. Essentially, aurora with multiple hosts for writing is a split brain scenario.

To handle aurora failover or adding new nodes in the same region with sequential connections, we have connections that expire every minute but this aurora mode without load balancing would allow us to not expire connections either.

I'm opening as a feature request since as recommended in CONTRIBUTING.md and what what I can tell, this is a new feature. I would be happy to contribute this change as removing the host list shuffling doesn't appear to be that complicated. Most of the code is basically the same for AuroraListener and AuroraProtocol.