Fix/cherry pick missing commits from slapos005

Somehow 3 commits from https://lab.nexedi.com/nexedi/slapos.buildout/-/merge_requests/35 got omitted from subsequent rebases: their changes are in 3.0.1+slapos005 but not in 3.0.1+slapos006 nor 3.0.1+slapos007.

These are what fixes buildout-testing/software-py2.cfg tests, so without these Python2 tests started failing again.