AutoTest: generalize create default result

Add a pure virtual function to TestOutputReader returning
a pointer to a default constructed result.

Change-Id: Icd8090346f2c5115a7c548da7ba69ea54fe39fc4
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/autotest/testoutputreader.h

@@ -49,6 +49,8 @@ public:
 signals:
     void newOutputAvailable(const QByteArray &output);
 protected:
+    virtual TestResultPtr createDefaultResult() const = 0;
+
     void reportResult(const TestResultPtr &result);
     QFutureInterface<TestResultPtr> m_futureInterface;
     QProcess *m_testApplication;  // not owned