Current the test harness provided by QpidBrokerTestCase utilises a UNIX shell script clean-dir to clean the broker's work
directory. This approach is less than ideal: spawning a separate process is relativity slow and this delays the test cycle, it presents
a barrier to running the test suite on Windows, and the approach is very sensitive to spaces within directory names (something that is preventing our use of Jenkins' matrix feature).
This change will remove the use of the shellscript and replace with the existing FileUtils.delete utility method.