title: "queue_declare" from pika returns 'None" when queried by setting passive="True" even when queue exists
body: <p>I am using pika for a consumer that consumes data from say queue "email"</p>
  
  <p><code>queue_declare</code> from pika  returns <code>None</code> when queried by setting <code>passive="True"</code> even when queue exists.</p>
  
  <p>I create the queue "email" using the web interface, and I can see that it exists (a third party is supposed to create it; I am only doing this for testing).</p>
  
  <p>Now in my program when I open the channel and before I start consuming on the email queue, I want to make sure that the queue already exists, so I set <code>passive</code> to be <code>True</code>:</p>
  
  <pre><code>def message(channel, envelope, properties, body):
      if send(envelope.routing_key, body):
          channel.basic_ack(envelope.delivery_tag)
          return
      print("Could not send message.")
  
  def channel_open(channel):
      QUEUES = CONFIG._defaults['queues']
      queuelist = QUEUES.split(",")
      for queuename in queuelist:
          result = channel.queue_declare(message,queue=queuename, passive=True)
          if not result:
              raise NameError("declare the queues specified "
                              "in default config section first")
          channel.basic_consume(queue=queuename, consumer_callback=message)
  </code></pre>
  
  <p>What I get in result is "<code>None</code>" while I was expecting to get an "<code>ok</code>" since queue already exists. Any pointers???  Is it because when the queue is declared using web UI the callback is not specified? I just want to know if queue exists but pika <code>queue_declare</code> function calls for a callback function as argument and complains when one is not given.</p>