ctr: move tasks, run to commands package

Signed-off-by: Jess Valarezo <valarezo.jessica@gmail.com>

cmd/ctr/commands/tasks/checkpoint.go

@@ -0,0 +1,51 @@
+package tasks
+
+import (
+	"fmt"
+
+	"github.com/containerd/containerd"
+	"github.com/containerd/containerd/cmd/ctr/commands"
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+var checkpointCommand = cli.Command{
+	Name:      "checkpoint",
+	Usage:     "checkpoint a container",
+	ArgsUsage: "[flags] CONTAINER",
+	Flags: []cli.Flag{
+		cli.BoolFlag{
+			Name:  "exit",
+			Usage: "stop the container after the checkpoint",
+		},
+	},
+	Action: func(context *cli.Context) error {
+		id := context.Args().First()
+		if id == "" {
+			return errors.New("container id must be provided")
+		}
+		client, ctx, cancel, err := commands.NewClient(context)
+		if err != nil {
+			return err
+		}
+		defer cancel()
+		container, err := client.LoadContainer(ctx, id)
+		if err != nil {
+			return err
+		}
+		task, err := container.Task(ctx, nil)
+		if err != nil {
+			return err
+		}
+		var opts []containerd.CheckpointTaskOpts
+		if context.Bool("exit") {
+			opts = append(opts, containerd.WithExit)
+		}
+		checkpoint, err := task.Checkpoint(ctx, opts...)
+		if err != nil {
+			return err
+		}
+		fmt.Println(checkpoint.Name())
+		return nil
+	},
+}