[Tails-dev] RFC: Use homogenous Debian mirrors at build time…

Hi,

we're currently hard-coding very little about the Debian mirrors we
use at build time in our Git tree.

Historically, this was meant to allow people to choose their preferred
mirror (e.g. local mirror) and to cope with squid-deb-proxy's lack of
flexibility. Nowadays, most of us use apt-cacher-ng, that can rewrite
such URLs on the fly if needed (generally a bad idea, see below, but
oh well), so probably we don't need this flexibility anymore.

Besides, this level of flexibility has just hit us hard, by
introducing a bug (#8715) that has taken many hours to three of us to
debug.

More generally, our stuff will be more consistent, easier to
reproduce, and our QA process will be more reliable if we all use the
same mirrors at build time as the one we configure in the ISO.

So, I want to:

1. hard-code in auto/config all mirrors that shall be used at build time
2. update vagrant/provision/setup-tails-builder so that it doesn't
configure LB_*MIRROR*, and deconfigures them if present
3. update wiki/src/contribute/build.mdwn so that it doesn't advise to
set $LB*MIRROR*
4. update tails::builder so that it doesn't configure LB_*MIRROR*, and
deconfigures them if present

(Steps 1-3 are implemented already in
feature/8726-use-homogenous-Debian-mirrors-at-build-time.)

Thoughts? Use cases I've not thought of?

Cheers,
--
intrigeri