Except shacache, nexedi.org, pypi, slapos, etc
Also modify the defaul cache URLs to shacache
Allow nexedi.org, 10.0.x.x slap.vifib.com

Also make vm-bootstrap role depends on python3

It was always done like this but has been removed in a previous cleanup (c7183d54). No need anymore for the upload.yml playbook.

In old Debian 10, after the release of Debian 11, apt update is failing
like this if we don't add the option "--allow-releaseinfo-change":

root@debian:~# apt update
Get:1 http://security.debian.org/debian-security buster/updates InRelease [65.4 kB]
Get:2 http://http.us.debian.org/debian buster InRelease [122 kB]
E: Repository 'http://security.debian.org/debian-security buster/updates InRelease' changed its 'Suite' value from 'stable' to 'oldstable'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.

See merge request !154

new one already added in dc173ee3

See merge request !155

See merge request !153

Same as re6stnet@f1e95660

See merge request !151

On slower hosts it takes a bit more time to boot the ISO some times, which
results with not receiving the ESC key to disable the graphic screen, and so
not working installation.

The general idea is to provide a machine connected to re6st, registered as
computer in SlapOS Master and with thorwable user to work on it.

Starting from default installation some uneeded packages are removed, and
few expected ones are added in order to have common set of packages and use
scenarios across all installations.

It's not possible on Ubuntu/Focal

The goal is to use the newest re6st-node package that correctly enables
the re6stnet service. re6st-node package has been fixed with
re6stnet@5bdb32e6
and 6972e11f

See merge request !148

Packer can be run on slow machines, give them time to do the job.

Only shacache assures stable URLs for reproducible builds.