QPID-5721: [Java Broker] Improve test coverage for default attributes, and attributes whose values are computed from context variables.

Also fixed defect so that a context attributes are resolved first, so that other attribute values may be calculated from context variables
set on the same object.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1600657 13f79535-47bb-0310-9956-ffa450edef68