Stabilize flake8 tests on 3.26 branch Use basepython=python2 or flake8 installed with python3 will raise "[F821] undefined name 'buffer'" Pin flake8 < 3.6 which has new checks that doesn't pass on our current code base.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js