Handle occasional error notification
Turris Updater runs 6 times a day. Sometimes for various reasons, an updater is not able to finish package cache update or similar operations.
This error leads to an error notifications all-the-time, which can be confusing and annoying. In fact, no big deal happens as the updater finishes its job next time (in a few hours).
We should handle these error notifications and send them only e.g. after all day without a successful update check. This would mitigate most of the false negative notifications for end users.