Make some minor changes to the server that will aid in setting up the test
environment.  The following changes are included:

- Allow the server root to be set using a Java property instead of an
  environment variable.  Under most circumstances, an environment variable will
  be used, but the system property may be used to override that.

- Create a system property that will cause all DirectoryThread objects to be
  created as daemon threads.  This can be called when running test cases so
  that if the server needs to be started it will stop running when all the
  tests are complete.