Reported via https://forum.vyos.io/t/dns-forward-system-error-in-1-3-rolling-202009170118/5911

Despite the fact that running verify on Config() is "bad" and "not as intended" the level of the configuration must match the keys that are checked by exits(). Re-set proper Config() level before querying the system nodes.

It's also a good candidate for get_config_dict() migration.