Make sure to keep other files in kube-proxy ConfigMap

The data was being overwritten with the new file map,
which caused the "config.conf" file to be deleted (!).

Compared to the original "kubeconfig.conf" generated,
the template also inserted an extra newline character.

pkg/minikube/bootstrapper/kubeadm/util.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"html/template"
+	"strings"
 
 	"github.com/golang/glog"
 	"github.com/pkg/errors"
@@ -175,11 +176,11 @@ func restartKubeProxy(k8s bootstrapper.KubernetesConfig) error {
 		return errors.Wrap(err, "executing kube proxy configmap template")
 	}
 
-	data := map[string]string{
-		kubeconfigConf: kubeconfig.String(),
+	if cfgMap.Data == nil {
+		cfgMap.Data = map[string]string{}
 	}
+	cfgMap.Data[kubeconfigConf] = strings.TrimSuffix(kubeconfig.String(), "\n")
 
-	cfgMap.Data = data
 	if _, err := client.CoreV1().ConfigMaps("kube-system").Update(cfgMap); err != nil {
 		return errors.Wrap(err, "updating configmap")
 	}