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>

image_store.go

@@ -74,9 +74,16 @@ func (s *remoteImages) Update(ctx context.Context, image images.Image, fieldpath
 	return imageFromProto(&updated.Image), nil
 }
 
-func (s *remoteImages) Delete(ctx context.Context, name string) error {
+func (s *remoteImages) Delete(ctx context.Context, name string, opts ...images.DeleteOpt) error {
+	var do images.DeleteOptions
+	for _, opt := range opts {
+		if err := opt(ctx, &do); err != nil {
+			return err
+		}
+	}
 	_, err := s.client.Delete(ctx, &imagesapi.DeleteImageRequest{
 		Name: name,
+		Sync: do.Synchronous,
 	})
 
 	return errdefs.FromGRPC(err)