This PR implements AdmissionOptions.ApplyTo

ApplyTo adds the admission chain to the server configuration the method lazily initializes a generic plugin
that is appended to the list of pluginInitializers.

apiserver.Config will hold an instance of SharedInformerFactory to ensure we only have once instance.
The field will be initialized in apisever.SecureServingOptions

pkg/master/master_test.go

@@ -37,6 +37,8 @@ import (
 	"k8s.io/apiserver/pkg/server/options"
 	serverstorage "k8s.io/apiserver/pkg/server/storage"
 	etcdtesting "k8s.io/apiserver/pkg/storage/etcd/testing"
+	"k8s.io/client-go/informers"
+	"k8s.io/client-go/kubernetes"
 	restclient "k8s.io/client-go/rest"
 	"k8s.io/kubernetes/pkg/api"
 	"k8s.io/kubernetes/pkg/api/testapi"
@@ -101,6 +103,12 @@ func setUp(t *testing.T) (*etcdtesting.EtcdTestServer, Config, *assert.Assertion
 		TLSClientConfig: &tls.Config{},
 	})
 
+	clientset, err := kubernetes.NewForConfig(config.GenericConfig.LoopbackClientConfig)
+	if err != nil {
+		t.Fatalf("unable to create client set due to %v", err)
+	}
+	config.GenericConfig.SharedInformerFactory = informers.NewSharedInformerFactory(clientset, config.GenericConfig.LoopbackClientConfig.Timeout)
+
 	return server, *config, assert.New(t)
 }