Add a common label to all resources on `kube apply'

You don't need to do this - maybe I wasn't clear on the previous comment, but if the object was properly decoded you should be able to add labels.  If the object is unrecognized, then you should perform the generic fallback.  But you shouldn't need to perform the generic cast here and then do reflection, you should only have to do:

```
switch t := obj.(type) {
case *api.ReplicationController:
  if err := mergeMaps(t.DesiredState.PodTemplate.Labels, src); err != nil {
  }
}
```