Start ping listener also for postgresql

Make use of the automatic connection disposal for
PostgreSQL as well.

oslo-incubator commit: 4a591eaafe035fa3fd508c910f057bfa8ff51005

Change-Id: I6e6adb612968639dbc8deae31e5409aac44e340e
Closes-Bug: 1288438
Merge "Start ping listener also for postgresql"