Description of periodic configuration options

Configuration option = Default value	Description
[DEFAULT]
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?