Handle timeouts from the AuthZ API

[ThiefMaster]

Right now we don't set any timeout, so if the AuthZ API is timing out, it quickly takes e.g. Indico down because all the requests end up waiting.

I think the best solution would be to set a timeout on all requests (maybe this can be done on the session level), but also "caching" timeouts for a short period (few seconds) so we don't try the same request again immediately. This is necessary because otherwise even a timeout of 1-2 seconds could easily hog uWSGI workers.