Run updater more often with random delay from initial execution

To make it more firm in packages sense we will now ship cron script as part of updater's package. Until now it was generated on first updater-ng installation. But that is problematic as this means that we are not directly controlling that file with our package and fixing it is complicated. But making it part of base system is also not ideal as that causes all routers to ask for updates at the same time. The solution is to delay update of random amount of time.