Disable protobuf codec in aggregated apiserver

[lukasfrank]

In order to remove these errors in the api server, disable protobuf codec:

E0929 08:08:17.910811       1 writers.go:122] apiserver was unable to write a JSON response: object *v1alpha1.LoadBalancerList does not implement the protobuf marshalling interface and cannot be encoded to a protobuf message
E0929 08:08:17.962945       1 writers.go:122] apiserver was unable to write a JSON response: object *v1alpha1.InstanceList does not implement the protobuf marshalling interface and cannot be encoded to a protobuf message
E0929 08:08:18.797877       1 writers.go:122] apiserver was unable to write a JSON response: object *v1alpha1.NATGatewayList does not implement the protobuf marshalling interface and cannot be encoded to a protobuf message
E0929 08:08:18.853380       1 writers.go:122] apiserver was unable to write a JSON response: object *v1alpha1.LoadBalancerRoutingList does not implement the protobuf marshalling interface and cannot be encoded to a protobuf message