Update clientset generator to use RESTClient interface instead of the RESTClient data type

pkg/client/unversioned/testclient/testclient.go

@@ -527,3 +527,7 @@ func (c *FakeDiscovery) ServerVersion() (*version.Info, error) {
 	versionInfo := version.Get()
 	return &versionInfo, nil
 }
+
+func (c *FakeDiscovery) RESTClient() restclient.Interface {
+	return nil
+}