Provide a way to stop Sonar Server programmatically

In order to help writing integration tests we need to have a way to ask Sonar Server to stop properly.
When property -Dsonar.shutdownToken=<token> is defined before starting Sonar Server then Jetty ShutdownHandler should be added and configured. Then the URL http://<sonar server>/shutdown?token=<token> could be called from the same host to ask Sonar Server to stop.
Note that by default the property should not be defined.