[SecurityBundle] fixed error_log() being called during functional tests

src/Symfony/Bundle/SecurityBundle/Tests/Functional/app/config/framework.yml

@@ -11,4 +11,7 @@ framework:
         default_locale: en
         lifetime:       3600
         auto_start:     true
-        storage_id: session.storage.filesystem
+        storage_id: session.storage.filesystem
+
+services:
+    logger: { class: Symfony\Component\HttpKernel\Log\NullLogger }