// returns error if it find extra or superfluous keys.
func CheckValidKeys(subSys string, kv KVS, validKVS KVS, deprecatedKeys ...string) error {
	nkv := KVS{}
	for _, kv := range kv {
		// Comment is a valid key, its also fully optional
		// ignore it since it is a valid key for all
		// sub-systems.
		if kv.Key == Comment {
			continue
		}
		var skip bool
		for _, deprecatedKey := range deprecatedKeys {