cf https://gitlab.com/gitlab-org/gitlab/-/issues/221221#note_363464695

fix #2

Cube-doctor proposes as default image python 3.7 this is not compatible with python2

integrate when https://forge.extranet.logilab.fr/logilab/infra/dockerfiles/-/merge_requests/24
has been published

pytest-html is installed on the system, and not available in the tox
environment. Thus this commit should be backout.

closes: #3