jcr2vfs: add jbpm-bpmn2 into droolsjbpm uberjar

 * the jcr2vfs migration tool requires the jbpm-bpmn2 in version 5.x.
   This change makes sure correct version is included directly in the
   uberjar and does not have to listed in the jcr2vfs pom
 * also changed the ${project.version} to ${drools.version}; although
   they are the same, the drools.version better reflects the
   usage here