Revert "upgrade gunicorn 19.0 and make upgrade"

This reverts commit f6c215ae5b.

common/djangoapps/track/views/__init__.py

@@ -96,8 +96,6 @@ def server_track(request, event_type, event, page=None):
     except:
         username = "anonymous"
 
-    host_header = 'HTTP_HOST' if request is not None and 'HTTP_HOST' in request.META else 'SERVER_NAME'
-
     # define output:
     event = {
         "username": username,
@@ -110,7 +108,7 @@ def server_track(request, event_type, event, page=None):
         "agent": _get_request_header(request, 'HTTP_USER_AGENT').decode('latin1'),
         "page": page,
         "time": datetime.datetime.utcnow().replace(tzinfo=pytz.utc),
-        "host": _get_request_header(request, host_header),
+        "host": _get_request_header(request, 'SERVER_NAME'),
         "context": eventtracker.get_tracker().resolve_context(),
     }