[devtools] Make timeout error in qunit tests configurable and use SkipTest in test_jscript.py This is grafted from 87443f279b0f in default branch (got tired of CI failing because of these unreliable tests).

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))