[pkg] Do not install sql scripts in <prefix>/share/cubicweb/schemas These are already site-packages along with cubicweb package.

[devtools/qunit] Retain firefox process stdout to eventually print it The bare RuntimeError that gets emitted upon timeout does not help much to diagnose the problem. Let's see if we can get more information from stdout by not dropping it.

[devtools/qunit] Turn FirefoxHelper into a context manager So that stop() method always gets called. Also ensure temporary directory created on __init__ gets deleted as well upon exit.