[PATCH 6/7] docker: add Python3.6 to image

[Stephen Finucane]

On Thu, 2018-01-25 at 13:43 +1100, Daniel Axtens wrote:
> This is needed to support py3.6-django111 in tox - otherwise tox
> fails.
> 
> Python3.6 is not in Xenial, so this - irritatingly - requires pulling
> in either a PPA, or the package from Artful. PPAs are icky, so pull
> it in from Artful.
> 
> We can either add an Artful repo (like we do for Trusty to pull in
> python3.4), or move the image to Artful and add in the Xenial repo
> to get python3.5. It's more efficient to move the entire image to
> Artful and pull in 3.5 from Xenial - otherwise most packages get
> downloaded from Artful anyway. It does mean we're going to need to
> move again to Bionic in a few months, but we'll just have to deal.
> 
> Signed-off-by: Daniel Axtens <dja at axtens.net>

I do wish Ubuntu shipped multiple Python versions the way Fedora does
but alas, it does not. In any case, this seems fine to me. We should
definitely bump this to 18.04 and use the 2.0 format Dockerfile once
18.04 is out.

Reviewed-by: Stephen Finucane <stephen at that.guru>