[knox] Disabled the MultipleProxyMiddleware for py2 (#3021)

The middleware is needed only on py3 and is interfering when
authenticating with knox. We are stripping out the gateway host's
header information and that is why it is failing the match
with proxy_hosts config.

desktop/core/src/desktop/settings.py

@@ -803,6 +803,8 @@ MODULES_TO_PATCH = (
 
 if sys.version_info[0] > 2:
   MIDDLEWARE.append('axes.middleware.AxesMiddleware')  # AxesMiddleware should be the last middleware in the MIDDLEWARE list.
+else:
+  MIDDLEWARE.remove('desktop.middleware.MultipleProxyMiddleware')
 
 try:
   import hashlib