title: Dialogflow_v2 sessions are slow
body: <br>
  I followed the official Dialogflow client documentation.<br>
  I am trying to get some intents for my input messages.
  It takes like 30-40 seconds to get a response which is unacceptable for a chatbot.
  In my example I've sent 2 messages (or more) - "test" and "hello". <br> The first request took very long and the second response (or any other following) is instant. 
  It would be ok if the first request takes forever and the following are fast, but the session terminates after no user input and it starts again.
  How can I speed it up or keep the session client alive?
  <pre><code>def detect_intent_texts(project_id, session_id, texts, language_code):
  &quot;&quot;&quot;Returns the result of detect intent with texts as inputs.
  Using the same `session_id` between requests allows continuation
  of the conversation.&quot;&quot;&quot;
  import dialogflow_v2 as dialogflow
  session_client = dialogflow.SessionsClient()
  
  session = session_client.session_path(project_id, session_id)
  print('Session path: {}\n'.format(session))
  
  for text in texts:
      text_input = dialogflow.types.TextInput(
          text=text, language_code=language_code)
  
      query_input = dialogflow.types.QueryInput(text=text_input)
      try:
          response = session_client.detect_intent(session=session, query_input=query_input)
      except InvalidArgument:
          raise
  
      print('=' * 20)
      print('Query text: {}'.format(response.query_result.query_text))
      print('Detected intent: {} (confidence: {})\n'.format(
          response.query_result.intent.display_name,
          response.query_result.intent_detection_confidence))
      print('Fulfillment text: {}\n'.format(
          response.query_result.fulfillment_text))
  </code></pre>
  <pre><code>if __name__ == '__main__':
      os.environ[&quot;GOOGLE_APPLICATION_CREDENTIALS&quot;] = 'private_key.json'
      DIALOGFLOW_PROJECT_ID = 'dialogflowslack'
      SESSION_ID = 'me'
      DIALOGFLOW_LANGUAGE_CODE = 'de'
      text_to_be_analyzed = [&quot;test&quot;, &quot;hallo&quot;]
  
      detect_intent_texts(
          DIALOGFLOW_PROJECT_ID, SESSION_ID, text_to_be_analyzed, DIALOGFLOW_LANGUAGE_CODE)
  </code></pre>