Fix tempest.conf permissions

Currently permissions are set to be root, but tempest runs as 'tempest'
user - and gets permission denied.

Change-Id: Ia3a8a2e780f95c6aa16a9d2483d987322741cfbf

ansible/roles/tempest/templates/tempest.json.j2

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