title: Openstack Python SDK - Glance does not return image MD5
body: <p>I'm trying to download an OpenStack image from glance using only the Openstack Python SDK, but I only get this error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/home/openstack/discovery/discovery.py", line 222, in &lt;module&gt;
      main(sys.argv[1:])
    File "/home/openstack/discovery/discovery.py", line 117, in main
      image_service.download_image(image)
    File "/usr/local/lib/python2.7/dist-packages/openstack/image/v2/_proxy.py", line 72, in download_image
      return image.download(self.session)
    File "/usr/local/lib/python2.7/dist-packages/openstack/image/v2/image.py", line 166, in download
      checksum = resp.headers["Content-MD5"]
    File "/usr/local/lib/python2.7/dist-packages/requests/structures.py", line 54, in __getitem__
      return self._store[key.lower()][1]
  KeyError: 'content-md5'
  </code></pre>
  
  <p>The weird part is that if I run the code using an IDE (PyCharm with remote debug) or as a script (python script.py -i ...) I get the error, but if I run each line using a python interpreter (ipython/python) the error does not happen! Have no idea why.</p>
  
  <p>Here is the code I'm using:</p>
  
  <pre><code>...
  image_name = node.name + "_" + time.strftime("%Y-%m-%d_%H-%M-%S")
  print "Getting data from", node.name
  compute_service.create_server_image(node, image_name)
  image = image_service.find_image(image_name)
  image_service.wait_for_status(image, 'active')
  fileName = "%s.img" % image.name
  
  with open(str(fileName), 'w+') as imgFile:
      imgFile.write(image.download(conn.image.session))
  ...
  </code></pre>
  
  <p>This code ends up calling the API in this file <code>/usr/local/lib/python2.7/dist-packages/openstack/image/v2/image.py</code>, with this method:</p>
  
  <pre><code>def download(self, session):
      """Download the data contained in an image"""
      # TODO(briancurtin): This method should probably offload the get
      # operation into another thread or something of that nature.
      url = utils.urljoin(self.base_path, self.id, 'file')
      resp = session.get(url, endpoint_filter=self.service)
  
      checksum = resp.headers["Content-MD5"]
      digest = hashlib.md5(resp.content).hexdigest()
      if digest != checksum:
          raise exceptions.InvalidResponse("checksum mismatch")
  
      return resp.content
  </code></pre>
  
  <p>The resp.headers variable has no key "Content-MD5". This is the value I found for it:</p>
  
  <pre><code>{'Date': 'Thu, 01 Sep 2016 20:17:01 GMT', 'Transfer-Encoding': 'chunked', 
   'Connection': 'keep-alive', 'Content-Type': 'application/octet-stream', 
   'X-Openstack-Request-Id': 'req-9eb16897-1398-4ab2-9cd4-45706e92819c'}
  </code></pre>
  
  <p>But according to the REST API documentationm the response should return with the key Content-MD5:
  <a href="http://developer.openstack.org/api-ref/image/v2/?expanded=download-binary-image-data-detail" rel="nofollow">http://developer.openstack.org/api-ref/image/v2/?expanded=download-binary-image-data-detail</a></p>
  
  <p>If I just comment the MD5 check the download works fine, but this is inside the SDK so I can't/shouldn't change it. Anyone have any suggestion on how to achieve this using the OpenStack Python SDK? Is this an SDK bug?</p>