QmlCppDebugger: Shutdown engine on port busy

Shutdown the debugger engines when the qmljsdebugger port
is busy.

Change-Id: If7f470b04bae26f3bac11863f697b260b463ca4e
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/plugins/debugger/qml/qmlcppengine.cpp

@@ -790,6 +790,8 @@ void QmlCppEngine::slaveEngineStateChanged
                 QTC_ASSERT(state() == InferiorRunRequested, qDebug() << state());
                 notifyInferiorRunOk();
             }
+        } else if (newState == EngineRunFailed) {
+            d->m_cppEngine->quitDebugger();
         }
     }
 }