Merge pull request #1011 from jitsi/adds-id-to-etherpad-iframe

Adds an id to etherpad iframe.

modules/UI/etherpad/Etherpad.js

 
         const iframe = document.createElement('iframe');
 
+        iframe.id = "etherpadIFrame";
         iframe.src = domain + name + '?' + options;
         iframe.frameBorder = 0;
         iframe.scrolling = "no";