Add ExternalName to ServiceSpec

ExternalName allows kubedns to return CNAME records for external
services. No proxying is involved.

See original issue at
https://github.com/kubernetes/kubernetes/issues/13748

Feature tracking at
https://github.com/kubernetes/features/issues/33

pkg/api/v1/zz_generated.deepcopy.go

@@ -3387,6 +3387,7 @@ func DeepCopy_v1_ServiceSpec(in interface{}, out interface{}, c *conversion.Clon
 		} else {
 			out.LoadBalancerSourceRanges = nil
 		}
+		out.ExternalName = in.ExternalName
 		return nil
 	}
 }