Configure jBPM unit tests to use connection pooling

Current jBPM unit tests already work with Narayana thanks to previous work done by mmacik@redhat.com and dhanak@redhat.com. The goal is to make sure jBPM works with DBPC2 pooling datasource with Narayana as it was possible with previous TM impl (Bitronix).

There are not going to be added any tests focusing on connection pooling specifically, as this should be covered by Narayana + PDS + JWS integration tests.

Use case:
As a developer, I want to use embedded jBPM engine and still have the benefit of transactions and DB connection pooling similarly to running in Java EE container.