Make the CLI nicer
==================

Add a "auto-sbuild" pseudo-command that selects sbuild to build .dsc files (and
guess the command artifact output), this should help with #847805.

Refactoring
===========

To allow to run N builds instead of just 2.

Afterwards we can then implement Bernhard's algorithm #850284.

Misc
====

--no-clean-on-error doesn't work since we did the shell-script based
refactoring, fix it.

add a default Debian-reprotest user in the Debian packaging and make this cross-distro
