Slightly different approach for previous commit:

- ensure we can define the default server URL to use, and actually
  use this when reconfiguring the discovery handler;
- also make the discovery configuration update a little more smarter
  by not doing anything if nothing has changed from the defaults.



git-svn-id: https://svn.apache.org/repos/asf/ace/trunk@1586521 13f79535-47bb-0310-9956-ffa450edef68