kubeadm: always use a short timeout for clientset creation

ToClientSet() in kubeconfig.go creates a clientset from
the passed Config object (kubeconfig). For IP addresses
that are not reachable e.g. Get() calls for ConfigMaps
can block for a few minutes with the default timeout.

Modify the timeout to a shorter value by passing an override.

cmd/kubeadm/app/util/kubeconfig/kubeconfig.go

@@ -80,7 +80,8 @@ func ClientSetFromFile(path string) (*clientset.Clientset, error) {
 
 // ToClientSet converts a KubeConfig object to a client
 func ToClientSet(config *clientcmdapi.Config) (*clientset.Clientset, error) {
-	clientConfig, err := clientcmd.NewDefaultClientConfig(*config, &clientcmd.ConfigOverrides{}).ClientConfig()
+	overrides := clientcmd.ConfigOverrides{Timeout: "10s"}
+	clientConfig, err := clientcmd.NewDefaultClientConfig(*config, &overrides).ClientConfig()
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to create API client configuration from kubeconfig")
 	}