title: No server chosen by ReadPreferenceServerSelector
body: <p>I am using Mongodb Java async driver which is newly released. I am writing some simple test codes, which are:</p>
  
  <pre><code>MongoClient mongoClient = MongoClients.create("mongodb://192.168.1.162:27017");
  MongoDatabase database = mongoClient.getDatabase("mongodb1");
  MongoCollection&lt;Document&gt; collection = database.getCollection("t_test");
  collection.count(
            new SingleResultCallback&lt;Long&gt;() {
                @Override
                public void onResult(final Long count, final Throwable t) {
                    System.out.println(count);
                }
            });
  
  System.out.println("AAAAAAAAAAAAAAAAAAAAAAAAA------end”);
  </code></pre>
  
  <p>however, the callback function is not called, the console output is:</p>
  
  <blockquote>
    <p>2017-06-21 13:57:58  [ INFO ]  Cluster created with settings {hosts=[192.168.1.162:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms', maxWaitQueueSize=500}
    2017-06-21 13:57:58  [ DEBUG ]  Updating cluster description to  {type=UNKNOWN, servers=[{address=192.168.1.162:27017, type=UNKNOWN, state=CONNECTING}]
    2017-06-21 13:57:58  [ INFO ]  No server chosen by ReadPreferenceServerSelector{readPreference=primary} from cluster description ClusterDescription{type=UNKNOWN, connectionMode=SINGLE, all=[ServerDescription{address=192.168.1.162:27017, type=UNKNOWN, state=CONNECTING}]}. Waiting for 30000 ms before timing out</p>
  </blockquote>