Reduce disk usage

[guyou]

Hi,

I would suggest a small optimization. It is possible to avoid creating the debian.tgz by simply piping the tar creation and the docker import:

tar cz -C $chroot_dir . | docker import - $docker_image

Hope that help.

[dashohoxha]

I think that it is space+time optimization vs code readability.
Anyway, if you have tested this and you submit a patch (or pull request) I can merge it.