title: NiFi NiPyApi gives me errors
body: <p>I managed to get at Kerberos ticket and perform some task with canvas object, but I still face some issues. 
  I have wrapped the code into a class and have those 2 functions </p>
  
  <p>The first function <code>getBulletinBoard</code> retrieves all messages in the bulletin board  from NiFi in it works fine:</p>
  
  <pre><code>def getBulletinBoard(self):
      canvas_id = canvas.get_bulletin_board()
      return canvas_id
  </code></pre>
  
  <p>The second function Stop Processor should stop a processor doesn't work, I have hardcorded my processor id into this for test reason and tried various thing to make it work. </p>
  
  <pre><code>def stopProcessor(self):
      try:
          canvas.schedule_processor('d73136a7-6b8d-1914-a511-3c5acb2b5515',scheduled=False)
      except nifi.rest.ApiException as e:
          print(e.body)
          return None
  </code></pre>
  
  <p>The output for <code>StopProcessor</code> function is </p>
  
  <pre><code>Traceback (most recent call last):
  File "c:\Temp\nifi-rest\test1.py", line 176, in &lt;module&gt;
  n.stopProcessor()
  File "c:\Temp\nifi-rest\test1.py", line 162, in stopProcessor
  canvas.schedule_processor('d73136a7-6b8d-1914-a511-  3c5acb2b5515',scheduled=False)
  File "C:\python3.6_32\lib\site-packages\nipyapi\canvas.py", line 528, in  schedule_processor
  assert isinstance(processor, nipyapi.nifi.ProcessorEntity)
  </code></pre>
  
  <p>AssertionError</p>
  
  <p>I cannot figure out why this doesn't work.</p>