offering: low-level network stats and pgbouncer stats user support

[jhwillett]

Offering PR #105 back upstream.

Adds support for overriding pgbouncer low-level network settings.

Adds support for specifying a username and password to enable the pgbouncer stats interface.

We have been live in production on this for several weeks. Thanks for introducing me to bats.

[jhwillett]

I have updated #105 to include recent changes on master which removed stunnel and resolve conflicts.