[pyramid] Avoid shutting down the repository at exit if it's already shutting down For install `cubicweb-ctl pyramid` command will explicitly call `repo.shutdown()` so the atexit hook is redundant. Prevent the latter to be executed when the repository is already shutting down (otherwise one gets an assertion error).

cubicweb source: source-is-missing cubicweb/web/data/jquery.flot.js line length is * characters (>512)