RuntimeManager fails in CMT environments that cannot access java:comp/UserTransaction

When using jBPM embedded in EJB services layer with CMT in AS like Websphere, RuntimeManager like PerProcessInstanceRuntimeManager fails at initialization as it can't resolve java:comp/UserTransaction.

The code creates a org.drools.persistence.jta.JtaTransactionManager with null arguments that try to discover UserTransaction. Per spec UserTransaction it is not visible if we run under CMT, so the system raises an exception. IMO it must try to discover first if we have a TransactionManager in Environment and reuse it, or create a KieSpringTransactionManager if we are under a Spring context.