Because the periodic_interval config option is used in several
places, it is difficult to tune its value. This patch restricts
the use of periodic_interval to its original purpose and introduces
four new config options that may be tuned independently:
* backup_driver_init_check_interval
* backup_driver_status_check_interval
* scheduler_driver_init_wait_time
* backend_stats_polling_interval
Includes release note and upgrade check.
Change-Id: I498484b06cd379ad65f6f0d18aaaeb85214d4b1e
Closes-bug: #1823748