debugger: fix EngineSetupFailed path

Task-number: QTCREATORBUG-2837

src/plugins/debugger/debuggerengine.cpp

@@ -1178,7 +1178,7 @@ void DebuggerEngine::notifyEngineSetupFailed()
     setState(EngineSetupFailed);
     QTC_ASSERT(d->m_runControl, return);
     d->m_runControl->startFailed();
-    d->queueShutdownEngine();
+    setState(DebuggerFinished);
 }
 
 void DebuggerEngine::notifyEngineSetupOk()

src/plugins/debugger/debuggerplugin.cpp

@@ -172,6 +172,13 @@
 // Transitions marked by '*' are done asynchronously.
 // The GdbEngine->setupEngine() function is described in more detail below.
 //
+// The engines are responsible for local roll-back to the last
+// acknowledged state before calling notify*Failed. I.e. before calling
+// notifyEngineSetupFailed() any process started during setupEngine()
+// so far must be terminated.
+//
+//
+//
 //                        DebuggerNotReady
 //                               +
 //                      EngineSetupRequested