title: Python logger not printing out 'extra' dictionary info
body: <p>In my python code I pass a dictionary into the logger for example.</p>
  
  <pre><code>extra_info = {"test":"data"}
  logger.info("",extra=extra_info)    
  </code></pre>
  
  <p>My hope is to get the extra info to print and I assumed it was in the message but when I use this format</p>
  
  <pre><code>format=%(asctime)s %(levelname)s %(name)s: %(message)s
  </code></pre>
  
  <p>The extra_info content are not being printed.  I just get the following</p>
  
  <pre><code>2016/06/17 13:10:47 INFO test:
  </code></pre>