AutoTest: Use Utils::FilePath for files and directories

Still some missing bits as some QString members had different meanings
depending on their context.

Change-Id: Ib48eab54498974a26bbd5123cbffeefee5f7e79c
Reviewed-by: hjk <hjk@qt.io>

src/plugins/autotest/qtest/qttestframework.cpp

@@ -42,7 +42,7 @@ ITestTreeItem *QtTestFramework::createRootNode()
                 this,
                 QCoreApplication::translate("QtTestFramework",
                                             QtTest::Constants::FRAMEWORK_SETTINGS_CATEGORY),
-                QString(), ITestTreeItem::Root);
+                Utils::FilePath(), ITestTreeItem::Root);
 }
 
 const char *QtTestFramework::name() const