ISIS-326: fixes for Tomcat lookup from JNDI

* MessageBroker must be serializable, suspicion is that it without it being serializable tomcat throws exception causing transactions to abort
* DataNucleusPersistenceMechanism looks first for 'datanucleus.ConnectionFactoryName' (JNDI), else falls back to the JNDI.
ISIS-208: service Ids cannot be unique