AutoTest: Redo reporting of disabled tests

Provide a proper way of reporting disabled tests instead
of the hacky one.

Change-Id: Id3a775d57ac20c9db8ad0f504cb708021117aa2f
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/autotest/testrunner.h

@@ -70,6 +70,7 @@ signals:
     void testRunFinished();
     void requestStopTestRun();
     void testResultReady(const TestResultPtr &result);
+    void hadDisabledTests(int disabled);
 
 private:
     void buildProject(ProjectExplorer::Project *project);