title: Swift MQTT libmosquitto cleanSession set to false yet unable to set up a persistent subscription
body: <pre><code>client = MosquittoClient(clientId: "client1")
  client?.delegate = self
  client?.port = 1883
  client?.host = "someIPAddress"
  client!.cleanSession = false
  client?.connect()
  </code></pre>
  
  <p>libmosquitto is a objective c library that is bridged over into a swift project. So after setting the cleanSession to false, i am still unable to set up a persistent subscription or receive message when offline. </p>