Some minor updates to the patterns for PgPool-II meta-data queries.

This is based on the latest version installed via Ubuntu packages.

To make such testing a little simpler going forward, I have added a pgpool container to our Docker scripts.

It is still far from an ideal solution, because it does not treat all backends as equivalent, thinking that it must send updates to the master. Moreover, the error alluded to in the documentation no longer occurs. The SQL Layer now properly responds to `current_setting(‘transaction_isolation’)` with `serializable`, which further motivates the pool to send to the master. So there will be very little real load balancing.