(#22350) Adding a read database, useful for Postgres Hot Standby clusters

Postgres supports Hot Standby: http://wiki.postgresql.org/wiki/Hot_Standby which
uses one database for writes and another database for reads.  This commit adds that
features and some tests ensuring the isolation of the read database calls from
the write database calls
Wrap the two-db shutdown call in a with-connection to ensure the correct
connection is used when shutting down an hsql instance
Change the max # of db connections to 25 per pool, 25 for reads, 25 for writes
Merge pull request #685 from senior/ticket/master/22350-separate-read-db

(#22350) Adding a read database, useful for Postgres Hot Standby clusters