func parseImageName(image string) (imageName, error) {
	l := strings.Split(image, ":")
	if len(l) != 4 {
		return imageName{}, fmt.Errorf("image name %q not a valid format", image)
	}
	return imageName{l[0], l[1], l[2], l[3]}, nil
}
func parseImageName(image string) (imageName, error) {
	l := strings.Split(image, ":")
	if len(l) != 4 {
		return imageName{}, fmt.Errorf("image name %q not a valid format", image)
	}
	return imageName{l[0], l[1], l[2], l[3]}, nil
}
// parseImageName parses a publisher:offer:sku:version into those parts.