Invoke the Celery worker with `-Ofair`; fixes #329
Invoke the Celery worker with `-Ofair`; fixes #329

Should avoid worker subprocesses sitting idle despite many queued jobs. Other
change: remove time limit and tasks per child settings from the command line
since b6e30094 provides for them to be specified in environment variables

kobotoolbox/kobocat,kobotoolbox/kobocat,kobotoolbox/kobocat,kobotoolbox/kobocat