Add list option for "minikube node" command

Add option to list the nodes.
So far there was no "minikube node list" command.

cmd/minikube/cmd/node.go

@@ -27,6 +27,6 @@ var nodeCmd = &cobra.Command{
 	Short: "Node operations",
 	Long:  "Operations on nodes",
 	Run: func(cmd *cobra.Command, args []string) {
-		exit.UsageT("Usage: minikube node [add|start|stop|delete]")
+		exit.UsageT("Usage: minikube node [add|start|stop|delete|list]")
 	},
 }

cmd/minikube/cmd/node_list.go

@@ -0,0 +1,58 @@
+/*
+Copyright 2020 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"os"
+	"fmt"
+
+	"github.com/golang/glog"
+	"github.com/spf13/cobra"
+	"k8s.io/minikube/pkg/minikube/driver"
+	"k8s.io/minikube/pkg/minikube/exit"
+	"k8s.io/minikube/pkg/minikube/mustload"
+)
+
+var nodeListCmd = &cobra.Command{
+	Use:   "list",
+	Short: "List nodes.",
+	Long:  "List existing Minikube nodes.",
+	Run: func(cmd *cobra.Command, args []string) {
+		if len(args) != 0 {
+			exit.UsageT("Usage: minikube node list")
+		}
+
+		cname := ClusterFlagValue()
+		_, cc := mustload.Partial(cname)
+
+		if len(cc.Nodes) < 1 {
+			glog.Warningf("Did not found any Minikube node.")
+		} else {
+			glog.Infof("%v", cc.Nodes)
+		}
+
+		for _, n := range cc.Nodes {
+			machineName := driver.MachineName(*cc, n)
+			fmt.Printf("%s\n", machineName)
+		}
+		os.Exit(0)
+	},
+}
+
+func init() {
+	nodeCmd.AddCommand(nodeListCmd)
+}