ProjectExplorer: Move re-runnable decision to RunWorkers

A RunControl is re-runnable if all its workers are,
a RunWorker is re-runnable if it's Stopped and unless it
says otherwise.

Also ensure SimpleTargetRunner only reportStop() once
per run and make process error message re-usable.

Change-Id: I73f5fb724d3026ceb81d5e32a3a71b4814b2bca9
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/debuggerruncontrol.h

@@ -82,11 +82,14 @@ public:
     int portsUsedByDebugger() const;
 
     void appendSolibSearchPath(const QString &str);
+
 signals:
     void aboutToNotifyInferiorSetupOk();
 
 private:
-    Internal::DebuggerEngine *m_engine = nullptr; // Master engine
+    void setupEngine();
+
+    QPointer<Internal::DebuggerEngine> m_engine; // Master engine
     Internal::DebuggerRunParameters m_runParameters;
     QStringList m_errors;
     bool m_isDying = false;