QPID-6292: [Java Broker Tests] Refactor AbstractConfiguredObjects unit tests to use several smaller test models

We now have two test models:

* 'singleton' with a single object - used for tests around the behaviour of attributes, context variables etc
* 'hierarchy' with a hierarchy of objects - used to test parent/child interactions, supported child types, and
   managed interfaces.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1648393 13f79535-47bb-0310-9956-ffa450edef68