plugin XEP-0353: fix jingle initiation on disco "Service Unavailable" error: When requesting disco info on a bare jid which is not in our roster, server may return "Service Unavailable" (to avoid leaking valid JIDs). In this case, the initiation was failing, this is now fixed by using empty categories in this case.

these certificates are used for demo purpose only. Those must be the same as in
backend_e2e (they are generated there)