AutoTest: Make test tree root items checkable

This allows (de)selecting of all test cases of a specific test
framework.

Change-Id: I21357d3dbcfce73387f157b1b40686f437fa260b
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/autotest/testtreeview.cpp

@@ -82,6 +82,10 @@ void TestTreeView::changeCheckStateAll(const Qt::CheckState checkState)
                     item->setChecked(checkState);
             }
         }
+        if (count == 0) {
+            if (auto item = static_cast<TestTreeItem *>(currentRootIndex.internalPointer()))
+                item->setChecked(checkState);
+        }
         emit dataChanged(currentRootIndex, last);
     }
 }