This patch series make a couple cosmetic/performance changes to the
docker package, and then goes on to patch the references to the
docker-proxy binary and the xz compression tool.

Prior to this patch, importing a docker image compressed using xz such
as in:

--8<---------------cut here---------------start------------->8---
docker load < some-docker-image.tar.xz
--8<---------------cut here---------------end--------------->8---

Would fail unless xz was found in the system's profile.

Thanks,

Maxim