Add support for clustered pools

[JohnAD]

Currently, the connection pool is limited to a single named destination server.

I want to add:

• support for querying a cluster of servers (noted in the URL) to see which one should be the current primary.

• support for a secondary read-only pool for better performance for reads that do not have to be as "true" as a primary read. To use a secondary read, a parameter would be added to getNextConnection to make it purposefully explicit.