Refactor internal API for Pods to match v1beta3

```
if err := latest.Codec.DecodeInto(...); err != nil {
  t.Fatalf("unexpected error: %v", err)
}
```

----- Original Message -----
> > @@ -544,10 +536,11 @@ func TestEtcdUpdatePodScheduled(t *testing.T) {
> >  	if err != nil {
> >  		t.Fatalf("Unexpected error: %v", err)
> >  	}
> > -	var list api.ContainerManifestList
> > +	var list api.BoundPods
> >  	latest.Codec.DecodeInto([]byte(response.Node.Value), &list)
> 
> There is a DeepEqual between the pod being updated and the list of BoundPods
> returned from the API call.
> 
> This is already doing what you suggest.
> 
> ---
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> https://github.com/GoogleCloudPlatform/kubernetes/pull/2097/files#r20471390