[Piglit] add compression support for file backends

[Ilia Mirkin]

On Wed, Jul 1, 2015 at 7:04 PM, Dylan Baker <baker.dylan.c at gmail.com> wrote:
> This adds a couple more unit tests, and a few fixes to the last version
> of this series, with the notable addition being support xz compression
>
> Ilia: how would you feel about dropping shell support and just using
> backports.lzma or not having xz support?

No one's going to have it... I do see it in portage though. But I also
don't immensely see the problem with just supporting shelling out to
the binary. But I also haven't read the code yet :)