Upgrade commons-dbcp to latest commons-dbcp2

DBCPConnectionPool currently uses Commons DBCP 1.4. There have been many improvements and a major release since then, at the time of this writing the latest version is 2.5.0.

This Jira proposes to upgrade the version of commons-dbcp to commons-dbcp2 version 2.5.0 in order to benefit from the improvements/additions. This will involve some code changes in addition to the updated dependencies, as the API has changed slightly to use different terminology e.g.