NO-JIRA: Rationalised unit test build
- Made an empty list of unit tests to build actually build all tests
  and made the default list empty, this gives much better behaviour
  in the usual case when adding and removing tests
- Also sorted list of unit tests

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1446233 13f79535-47bb-0310-9956-ffa450edef68