In particular LocMemCache doesn't have this option.

For more details, see:

http://stackoverflow.com/questions/23358787/memcache-get-returns-wrong-object-celery-django

Part of the file name template is eaten up by Python's `%` formatting,
resulting in log files missing the `s` of "stderr" and "stdout".

supervisord as well as all the processes it controls are run as
`{{ common_web_user }}`. This allows us to connect to it as that
user which allows us to manage the processes as www-data, instead
of root.

Since xqueue has its own set of dependencies, using a dedicated
virtualenv allows to avoid potential dependencies conflicts when
several services are installed on the same instance.

To be used in conjonction with
https://github.com/antoviaque/xqueue/commit/303601ea9ffcbd30f6bb3e2b9a42d6f85fbcf6b3

This is necessary to be able to get several services using the
`/opt/wwc/env.json` & `/opt/wwc/auth.json` files. The configuration
files would get overwitten when this is used by several different
services cohabiting on a single instance

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