Fix: viper.UnmarshalKey ignores defaults

This seems to be a bug in viper, as soon as we're working with subkeys, things fall apart

service/config.go

@@ -34,7 +34,13 @@ func SetConfigDefaults() {
 }
 
 func LoadConfig() {
-	viper.UnmarshalKey("Service", &C)
+	// Does not work with partially overrides, only GetXXX does resolve the subkeys correctly
+	// https://github.com/spf13/viper/issues/798
+	// https://github.com/spf13/viper/issues/309
+	// viper.UnmarshalKey("Service", &C)
+	C.DNS.Server = viper.GetString("Service.DNS.Server")
+	C.DNS.DefaultTTL = viper.GetUint32("Service.DNS.DefaultTTL")
+	C.Users.ConfigDir = viper.GetString("Service.Users.ConfigDir")
 }
 
 func (obj *config) PrettyPrint() string {