Update vendor files to point to kubernetes-1.12.0-beta.1

vendor/k8s.io/client-go/plugin/pkg/client/auth/exec/exec.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -36,6 +37,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/runtime/serializer"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/client-go/pkg/apis/clientauthentication"
 	"k8s.io/client-go/pkg/apis/clientauthentication/v1alpha1"
 	"k8s.io/client-go/pkg/apis/clientauthentication/v1beta1"
@@ -51,9 +53,9 @@ var codecs = serializer.NewCodecFactory(scheme)
 
 func init() {
 	v1.AddToGroupVersion(scheme, schema.GroupVersion{Version: "v1"})
-	v1alpha1.AddToScheme(scheme)
-	v1beta1.AddToScheme(scheme)
-	clientauthentication.AddToScheme(scheme)
+	utilruntime.Must(v1alpha1.AddToScheme(scheme))
+	utilruntime.Must(v1beta1.AddToScheme(scheme))
+	utilruntime.Must(clientauthentication.AddToScheme(scheme))
 }
 
 var (
@@ -178,21 +180,10 @@ func (a *Authenticator) UpdateTransportConfig(c *transport.Config) error {
 		return &roundTripper{a, rt}
 	}
 
-	getCert := c.TLS.GetCert
-	c.TLS.GetCert = func() (*tls.Certificate, error) {
-		// If previous GetCert is present and returns a valid non-nil
-		// certificate, use that. Otherwise use cert from exec plugin.
-		if getCert != nil {
-			cert, err := getCert()
-			if err != nil {
-				return nil, err
-			}
-			if cert != nil {
-				return cert, nil
-			}
-		}
-		return a.cert()
+	if c.TLS.GetCert != nil {
+		return errors.New("can't add TLS certificate callback: transport.Config.TLS.GetCert already set")
 	}
+	c.TLS.GetCert = a.cert
 
 	var dial func(ctx context.Context, network, addr string) (net.Conn, error)
 	if c.Dial != nil {