Use separate counters for pre- and post-patch reboots. (#788) `RebootCount` was used only for forcing post-patch reboots via `RebootConfig = always`, but incremented for every reboot. As a result, the forced post-patch reboot was skipped if pre-patch reboot was required. This changes it to count pre-patch reboots separately. In addition, it adds a guard against the endless patch reboot loops. The limit was selected through common sense. Closes: #755