Preload containerd images

[medyagh]

implement preload for containerd for overlay2.
by generating a tar ball with all images for a kubernetes version, similar to our docker runtime.

[afbjorklund]

by generating a tar ball with all images for a kubernetes version, similar to our docker runtime.

That is not how the current preload works, though. It just dumps the /var/lib internals (the guts)

func createImageTarball(tarballFilename string) error {
	// directories to save into tarball
	dirs := []string{
		fmt.Sprintf("./lib/docker/%s", dockerStorageDriver),
		"./lib/docker/image",
		"./lib/minikube/binaries",
	}
	args := []string{"exec", profile, "sudo", "tar", "-I", "lz4", "-C", "/var", "-cvf", tarballFilename}
	args = append(args, dirs...)
	cmd := exec.Command("docker", args...)
	cmd.Stdout = os.Stdout
	if err := cmd.Run(); err != nil {
		return errors.Wrapf(err, "tarball cmd: %s", cmd.Args)
	}
	return nil
}

So in this case, it should dump the /var/lib/containerd instead of /var/lib/docker.

It is still a good idea though (generating the image-only tarball), will add a separate issue for it

[afbjorklund]

Nobody uses containerd with minikube, and if they do - they could survive without the preload

So lowered the priority.

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