Svc REST: Overhaul Create test wrt dual-stack

This includes a few cases.

1) TestCreateIgnoresIPFamilyForExternalName: Prove that ExternalName is
ignored for dual-stack.  A small set of test cases were chosen to
demonstrate.

2) TestCreateIgnoresIPFamilyWithoutDualStack: Prove that when the
dual-stack gate is off, all services are ignored for dual-stack.  A
small set of test cases were chosen to demonstrate

3) TestCreateInitIPFields: Run over a huge array of test cases for
dual-stack.  This was generated by this program:
https://gist.github.com/thockin/cccc9c9a580b4830ee0946ddd43eeafe and
then updated by hand.

pkg/api/service/testing/make.go

@@ -113,6 +113,29 @@ func MakeServicePort(name string, port int, tgtPort intstr.IntOrString, proto ap
 	}
 }
 
+// SetHeadless sets the service as headless and clears other fields.
+func SetHeadless(svc *api.Service) {
+	SetTypeClusterIP(svc)
+	svc.Spec.ClusterIP = api.ClusterIPNone
+}
+
+// SetSelector sets the service selector.
+func SetSelector(sel map[string]string) Tweak {
+	return func(svc *api.Service) {
+		svc.Spec.Selector = map[string]string{}
+		for k, v := range sel {
+			svc.Spec.Selector[k] = v
+		}
+	}
+}
+
+// SetClusterIP sets the service ClusterIP fields.
+func SetClusterIP(ip string) Tweak {
+	return func(svc *api.Service) {
+		svc.Spec.ClusterIP = ip
+	}
+}
+
 // SetClusterIPs sets the service ClusterIP and ClusterIPs fields.
 func SetClusterIPs(ips ...string) Tweak {
 	return func(svc *api.Service) {