[core] Default gunicorn workers to one

This avoid lost query handles for now.

Author: romainr

desktop/conf.dist/hue.ini

@@ -67,7 +67,7 @@
   ## gunicorn_work_class=eventlet
 
   # The number of Gunicorn worker processes. If not specified, it uses: (number of CPU * 2) + 1.
-  ## gunicorn_number_of_workers=None
+  ## gunicorn_number_of_workers=1
 
   # Webserver runs as this user
   ## server_user=hue

desktop/conf/pseudo-distributed.ini.tmpl

@@ -71,7 +71,7 @@
   ## gunicorn_work_class=eventlet
 
   # The number of Gunicorn worker processes. If not specified, it uses: (number of CPU * 2) + 1.
-  ## gunicorn_number_of_workers=None
+  ## gunicorn_number_of_workers=1
 
   # Webserver runs as this user
   ## server_user=hue

desktop/core/src/desktop/conf.py

@@ -163,7 +163,7 @@ def get_slack_bot_user_token():
   key="gunicorn_number_of_workers",
   help=_("The number of Gunicorn worker processes. If not specified, it uses: (number of CPU * 2) + 1."),
   type=int,
-  default=None)
+  default=1)
 
 HTTP_HOST = Config(
   key="http_host",