Support for xzip

[Suirtimed]

It was brought to my attention that xzip may achieve better results than bzip.

It appears that docker supports xzip: https://docs.docker.com/v1.8/reference/builder/

There is also a ruby gem that supports xzip: https://github.com/quintus/ruby-xz/

[tjmcs]

Added a related issue Issue #410 to the Hanlon project to track this one (since that's where the work will actually be done); when that issue is closed this one can be closed as well