Tests: JettyFeature shutdown deadlock

The following deadlock can occur when using the JettyFeature:

• jetty server is lauched
• test thread does a jetty request then returns quickly
• jetty thread takes some time to do its work
• test thread shuts down the runtime, while synchonizing on the ComponentManagerImpl instance in:
  • ComponentManagerImpl.shutdown
  • ComponentManagerImpl.unregister for each component
• test thread gets to JettyComponent.deactivate, with above monitor held
  • this waits for all jetty threads to stop while doing Server.stop()
• jetty thread, still working, calls Framework.getService, which calls ComponentManagerImpl.getComponentProvidingService which does a synchronize on the ComponentManagerImpl instance

-> deadlock