335f0f2eab
This review allows periodic tasks to be enabled or disabled in the decorator, as well as by specifying an interval which is negative. The spacing between runs of a periodic task is now specified in seconds, with zero meaning the default spacing which is currently 60 seconds. There is also a new argument to the decorator which indicates if a periodic task _needs_ to be run in the nova-compute process. There is also a flag (run_external_periodic_tasks) which can be used to move these periodic tasks out of the nova-compute process. I also remove the periodic_interval flag to services, as the interval between runs is now dynamic based on the number of seconds that a periodic task wants to wait for its next run. For callers who want to twiddle the sleep period (for example unit tests), there is a create() argument periodic_interval_max which lets the period periodic_tasks() specifies be overridden. This is not exposed as a flag because I cannot see a use case for that. It is needed for unit testing however. DocImpact. Resolves bug 939087. Change-Id: I7f245a88b8d229a481c1b65a4c0f1e2769bf3901