Debugger: Do a hard shutdown when QML debugger is stopped

There is no point in trying to "gracefully" shutdown by waiting for the
application to hit the next line of JavaScript. The application might
never execute any more JavaScript.

Change-Id: Id531a2b23ce9aa12462e308f29106f8cefa67092
Task-number: QTCREATORBUG-16709
Reviewed-by: hjk <hjk@qt.io>