Merge pull request kubernetes#126649 from 0x5457/fix-panic

apiserver: declare kubeClient and dynamicClient as interface types to avoid panic

Author: k8s-ci-robot

staging/src/k8s.io/apiserver/pkg/server/options/recommended.go

@@ -120,8 +120,8 @@ func (o *RecommendedOptions) ApplyTo(config *server.RecommendedConfig) error {
 	if err := o.CoreAPI.ApplyTo(config); err != nil {
 		return err
 	}
-	var kubeClient *kubernetes.Clientset
-	var dynamicClient *dynamic.DynamicClient
+	var kubeClient kubernetes.Interface
+	var dynamicClient dynamic.Interface
 	if config.ClientConfig != nil {
 		var err error
 		kubeClient, err = kubernetes.NewForConfig(config.ClientConfig)