Move quota options to a config group.

As suggested in John Garbutt in I7e1986c5f11356060cc9db12605b1322c39e79c0,
move the quota config options into a config group of their own.

Change-Id: Ie06a370868f01fb9a1cc246a77d7823fac83e70e

nova/db/sqlalchemy/api.py

@@ -4510,7 +4510,7 @@ def _security_group_ensure_default(context):
                                 context.user_id,
                                 'security_groups',
                                 1, 0,
-                                CONF.until_refresh,
+                                CONF.quota.until_refresh,
                                 context.session)
         else:
             usage.update({'in_use': int(usage.first().in_use) + 1})