Add synchronous image delete

Synchronous image delete provides an option image delete to wait
until the next garbage collection deletes after an image is removed
before returning success to the caller.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

cmd/ctr/commands/images/images.go

@@ -270,8 +270,14 @@ var removeCommand = cli.Command{
 	Name:        "remove",
 	Aliases:     []string{"rm"},
 	Usage:       "remove one or more images by reference",
-	ArgsUsage:   "<ref> [<ref>, ...]",
+	ArgsUsage:   "[flags] <ref> [<ref>, ...]",
 	Description: "remove one or more images by reference",
+	Flags: []cli.Flag{
+		cli.BoolFlag{
+			Name:  "sync",
+			Usage: "Synchronously remove image and all associated resources",
+		},
+	},
 	Action: func(context *cli.Context) error {
 		client, ctx, cancel, err := commands.NewClient(context)
 		if err != nil {
@@ -282,8 +288,12 @@ var removeCommand = cli.Command{
 			exitErr    error
 			imageStore = client.ImageService()
 		)
-		for _, target := range context.Args() {
-			if err := imageStore.Delete(ctx, target); err != nil {
+		for i, target := range context.Args() {
+			var opts []images.DeleteOpt
+			if context.Bool("sync") && i == context.NArg()-1 {
+				opts = append(opts, images.SynchronousDelete())
+			}
+			if err := imageStore.Delete(ctx, target, opts...); err != nil {
 				if !errdefs.IsNotFound(err) {
 					if exitErr == nil {
 						exitErr = errors.Wrapf(err, "unable to delete %v", target)