Provide Test Helper Classes for Case Management and jBPM services

JBPM 6.x and 7.x provide the JbpmJUnitBaseTestCase class found in the link below, which allows us to easily bootstrap a jBPM environment for unit testing purposes. Currently this class does not cater for Case Management based processes thus this can be a lot of additional code to write. It would be useful to extend JbpmJUnitBaseTestCase to cater for Case Management base implementations and incorporate jbpm-services into the testing capabilities.

https://github.com/kiegroup/jbpm/blob/master/jbpm-test/src/main/java/org/jbpm/test/JbpmJUnitBaseTestCase.java

An example of one of Maciej's Case Management testing classes can be found here:

https://github.com/kiegroup/jbpm/blob/r7.7.0.Final/jbpm-case-mgmt/jbpm-case-mgmt-impl/src/test/java/org/jbpm/casemgmt/impl/util/AbstractCaseServicesBaseTest.java