Set owner of rally.conf to rally

This will solve the following issue when running the rally bootstrap
container:

oslo_config.cfg.ConfigFilesPermissionDeniedError: Failed to open some
config files: /etc/rally/rally.conf

TrivialFix

Change-Id: I90c840850ea0579e375a7c75f3192fe0387f4270

ansible/roles/rally/templates/rally.json.j2

@@ -4,7 +4,7 @@
         {
             "source": "{{ container_config_directory }}/rally.conf",
             "dest": "/etc/rally/rally.conf",
-            "owner": "root",
+            "owner": "rally",
             "perm": "0600"
         }
     ]