Update ctr containers and tasks command

This moves container and tasks commands under the containers and tasks
top level commands.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/ctr/task.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"text/tabwriter"
+
+	tasks "github.com/containerd/containerd/api/services/tasks/v1"
+	"github.com/urfave/cli"
+)
+
+var tasksCommand = cli.Command{
+	Name:    "tasks",
+	Usage:   "manage tasks",
+	Aliases: []string{"t"},
+	Flags: []cli.Flag{
+		cli.BoolFlag{
+			Name:  "quiet, q",
+			Usage: "print only the task id & pid",
+		},
+	},
+	Subcommands: []cli.Command{
+		taskAttachCommand,
+		taskCheckpointCommand,
+		taskExecCommand,
+		taskKillCommand,
+		taskPauseCommand,
+		taskPsCommand,
+		taskResumeCommand,
+		taskStartCommand,
+		taskDeleteCommand,
+	},
+	Action: func(context *cli.Context) error {
+		var (
+			quiet       = context.Bool("quiet")
+			ctx, cancel = appContext(context)
+		)
+		defer cancel()
+
+		client, err := newClient(context)
+		if err != nil {
+			return err
+		}
+		s := client.TaskService()
+		response, err := s.List(ctx, &tasks.ListTasksRequest{})
+		if err != nil {
+			return err
+		}
+		if quiet {
+			for _, task := range response.Tasks {
+				fmt.Println(task.ID)
+			}
+			return nil
+		}
+		w := tabwriter.NewWriter(os.Stdout, 4, 8, 4, ' ', 0)
+		fmt.Fprintln(w, "TASK\tPID\tSTATUS\t")
+		for _, task := range response.Tasks {
+			if _, err := fmt.Fprintf(w, "%s\t%d\t%s\n",
+				task.ID,
+				task.Pid,
+				task.Status.String(),
+			); err != nil {
+				return err
+			}
+		}
+		return w.Flush()
+	},
+}