N°2651 rollback gitignore for lib tests dirs

Too dangerous ! We'll work properly on this but for 2.8

lib/symfony/framework-bundle/Tests/Functional/app/Session/config.yml

@@ -0,0 +1,7 @@
+imports:
+    - { resource: ./../config/default.yml }
+
+services:
+    Symfony\Bundle\FrameworkBundle\Tests\Functional\Bundle\TestBundle\Controller\SubRequestController:
+        tags:
+            - { name: controller.service_arguments, action: indexAction, argument: handler, id: fragment.handler }