title: XMPP Smack 4.1.0 check is user is already registered
body: <p>Hi Im using the Smack XMPP library for android.</p>
  
  <p>I have figured out how to connect, login and create a user, but if I try to create an account with a username that already exist, i get a 'conflict' error, then if i change the username and try again, im locked out for about 10 mins, with a "not_acceptable - wait" error.</p>
  
  <p>So how would i check if the username exists before creating an account?</p>