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/quick/quicktestframework.cpp

@@ -42,7 +42,7 @@ ITestParser *QuickTestFramework::createTestParser()
 ITestTreeItem *QuickTestFramework::createRootNode()
 {
     return new QuickTestTreeItem(this, QCoreApplication::translate("QuickTestFramework", "Quick Test"),
-                                 QString(), ITestTreeItem::Root);
+                                 Utils::FilePath(), ITestTreeItem::Root);
 }
 
 const char *QuickTestFramework::name() const