Introduce ObjectConvertor for conversion to known API versions

Will allow clients to transform internal objects to a version
suitable for external output.

pkg/runtime/scheme.go

@@ -17,6 +17,7 @@ limitations under the License.
 package runtime
 
 import (
+	"fmt"
 	"reflect"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/conversion"
@@ -223,6 +224,23 @@ func (s *Scheme) Convert(in, out interface{}) error {
 	return s.raw.Convert(in, out)
 }
 
+// ConvertToVersion attempts to convert an input object to its matching Kind in another
+// version within this scheme. Will return an error if the provided version does not
+// contain the inKind (or a mapping by name defined with AddKnownTypeWithName). Will also
+// return an error if the conversion does not result in a valid Object being
+// returned.
+func (s *Scheme) ConvertToVersion(in Object, outVersion string) (Object, error) {
+	unknown, err := s.raw.ConvertToVersion(in, outVersion)
+	if err != nil {
+		return nil, err
+	}
+	obj, ok := unknown.(Object)
+	if !ok {
+		return nil, fmt.Errorf("the provided object cannot be converted to a runtime.Object: %#v", unknown)
+	}
+	return obj, nil
+}
+
 // EncodeToVersion turns the given api object into an appropriate JSON string.
 // Will return an error if the object doesn't have an embedded TypeMeta.
 // Obj may be a pointer to a struct, or a struct. If a struct, a copy