title: Issue with async library for Google Datastore
body: <p>I am using the library <a href="https://github.com/spotify/async-datastore-client" rel="nofollow">https://github.com/spotify/async-datastore-client</a> for async google datastore operations. When I run the following code it always output "Failure". I am testing this against my local development database. I am new to Google datastore so I am not sure what exactly is wrong although I have a gut feeling something is wrong with the datastore config (e.g do I need credentials, some other missing params?). I have not signed up for any Google services yet. I would just like to insert something into my local database and have it succeed using this library.</p>
  
  <pre><code>import com.spotify.asyncdatastoreclient.DatastoreConfig;
  import com.spotify.asyncdatastoreclient.Datastore;
  import com.spotify.asyncdatastoreclient.QueryBuilder;
  import com.spotify.asyncdatastoreclient.Insert;
  import com.spotify.asyncdatastoreclient.MutationResult;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.util.concurrent.FutureCallback;
  import com.google.common.util.concurrent.Futures;
  import com.google.common.util.concurrent.ListenableFuture;
  import io.vertx.core.AbstractVerticle;
  
  
  
  public class Main{
  
      public void initDB() throws Exception {
  
       final DatastoreConfig config = DatastoreConfig.builder()
      .requestTimeout(1000)
      .requestRetry(3)
      .host("http://localhost:8080")
      .dataset("async-test")
      //.credential(DatastoreHelper.getServiceAccountCredential(null, null))
      .build();
  
  final Datastore datastore = Datastore.create(config);
  
  final Insert insert = QueryBuilder.insert("employee", 1234567L)
      .value("fullname", "Fred Blinge")
      .value("age", 40);
  
  // for asynchronous call...
  final ListenableFuture&lt;MutationResult&gt; resultAsync = datastore.executeAsync(insert);
  
        Futures.addCallback(resultAsync, new FutureCallback&lt;MutationResult&gt;() {
        @Override
        public void onSuccess(final MutationResult result) {
            System.out.println("Success");
        }
  
        @Override
        public void onFailure(final Throwable throwable) {
            System.out.println("Failure");   
        }
      });
  
      }
  
  }
  </code></pre>