Introduce GroupVersioner for capturing desired target version

Convert single GV and lists of GVs into an interface that can handle
more complex scenarios (everything internal, nothing supported). Pass
the interface down into conversion.

pkg/runtime/unversioned_test.go

@@ -30,14 +30,13 @@ import (
 	"k8s.io/kubernetes/pkg/runtime"
 )
 
-var status = &unversioned.Status{
-	Status:  unversioned.StatusFailure,
-	Code:    200,
-	Reason:  unversioned.StatusReasonUnknown,
-	Message: "",
-}
-
 func TestV1EncodeDecodeStatus(t *testing.T) {
+	status := &unversioned.Status{
+		Status:  unversioned.StatusFailure,
+		Code:    200,
+		Reason:  unversioned.StatusReasonUnknown,
+		Message: "",
+	}
 
 	v1Codec := testapi.Default.Codec()
 
@@ -65,6 +64,12 @@ func TestV1EncodeDecodeStatus(t *testing.T) {
 }
 
 func TestExperimentalEncodeDecodeStatus(t *testing.T) {
+	status := &unversioned.Status{
+		Status:  unversioned.StatusFailure,
+		Code:    200,
+		Reason:  unversioned.StatusReasonUnknown,
+		Message: "",
+	}
 	// TODO: caesarxuchao: use the testapi.Extensions.Codec() once the PR that
 	// moves experimental from v1 to v1beta1 got merged.
 	expCodec := api.Codecs.LegacyCodec(extensions.SchemeGroupVersion)