FELIX-4561 - Unregistration fails sometimes:

- if the HttpService itself is stopping, it deregisters all of its
  servlets and filters. This causes the whiteboard service to also
  start deregistering its servlets & filters, causing exceptions in
  the HttpService;
- make the whiteboard unregister at best-effort, catching exceptions
  that occur during the unregistration & log a message instead;
- suppress throwing of exceptions when unregister is called on the
  HttpService while the bundle is stopping.



git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1634894 13f79535-47bb-0310-9956-ffa450edef68