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_delete.go

@@ -0,0 +1,33 @@
+package main
+
+import "github.com/urfave/cli"
+
+var taskDeleteCommand = cli.Command{
+	Name:      "delete",
+	Usage:     "delete a task",
+	ArgsUsage: "CONTAINER",
+	Action: func(context *cli.Context) error {
+		ctx, cancel := appContext(context)
+		defer cancel()
+		client, err := newClient(context)
+		if err != nil {
+			return err
+		}
+		container, err := client.LoadContainer(ctx, context.Args().First())
+		if err != nil {
+			return err
+		}
+		task, err := container.Task(ctx, nil)
+		if err != nil {
+			return err
+		}
+		status, err := task.Delete(ctx)
+		if err != nil {
+			return err
+		}
+		if status != 0 {
+			return cli.NewExitError("", int(status))
+		}
+		return nil
+	},
+}