Description of configuration options for periodic

Configuration option=Default value	Description
periodic_enable=True	(BoolOpt) enable periodic tasks
periodic_fuzzy_delay=60	(IntOpt) range of seconds to randomly delay when starting the periodic task scheduler to reduce stampeding. (Disable by setting to 0)
run_external_periodic_tasks=True	(BoolOpt) Some periodic tasks can be run in a separate process. Should we run them here?