Redmine#5339: add inventory update_interval to ensure CSV files are there; support SUSE

* add a `update_interval` parameter to each inventory package body
* as long at the patch and package list are missing, keep trying to regenerate them
* as soon as they are present, go to the 1-week update interval
* add a SUSE `inventory_zypper` method to do package and patch updates on SUSE