[devtools] Make timeout error in qunit tests configurable and use SkipTest in test_jscript.py The reason is that the latter tests quite often fail in our CI environment, possibly due to concurrent execution of the browser, and this makes it hard to identify a truly failing build there. So skip tests with a timeout error.

[check-manifest]
ignore =
  debian
  debian/*
  cubicweb.spec
  __pkginfo__.py