Add private message handler for breakout_rooms

Add the _onPrivateMessage handler when breakout_rooms is found in disco info.

modules/xmpp/xmpp.js

 
         if (this.avModerationComponentAddress
             || this.speakerStatsComponentAddress
-            || this.conferenceDurationComponentAddress) {
+            || this.conferenceDurationComponentAddress
+            || this.breakoutRoomsComponentAddress) {
             this.connection.addHandler(this._onPrivateMessage.bind(this), null, 'message', null, null);
         }
     }