discover STUN servers from disco requests
Submitted by Robert McQueen @ramcq
Assigned to Will Thompson @wjt
Description
Recent releases XMPP servers like OpenFire and Ejabberd come with STUN server plugins which get advertised in the server's disco responses. We should find such things and use them to set the STUN server and port used for Jingle calls if we didn't get one by doing the google:relay thing and the user didn't specify one.