title: google cloud datalab: reload set from bigquery leads to RespondNotReady
body: <p>Using Datalab for analysis, I need to sample data from bigquery. When I refresh my sample, I sometimes get this error:</p>
  
  <pre><code>/usr/lib/python2.7/httplib.pyc in getresponse(self, buffering)
     1059         #
     1060         if self.__state != _CS_REQ_SENT or self.__response:
  -&gt; 1061             raise ResponseNotReady()
     1062 
     1063         args = (self.sock,)
  
  ResponseNotReady: 
  </code></pre>
  
  <p>This behaviour happens randomly while iterating (100 iterations).</p>
  
  <p>Any clue?</p>