AutoTest: Code cosmetics

* use nullptr
* override
* remove old style casts
* fix most of the code model warnings

Change-Id: Ia08e846f9326ae28ca7e7d66748e25a8b817b9b1
Reviewed-by: Xing Xiong
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/autotest/autotestplugin.h

@@ -46,7 +46,7 @@ class AutotestPlugin : public ExtensionSystem::IPlugin
 
 public:
     AutotestPlugin();
-    ~AutotestPlugin();
+    ~AutotestPlugin() override;
 
     bool initialize(const QStringList &arguments, QString *errorString) override;
     void extensionsInitialized() override;