T7239: test of bootloader's bootcounter mechanism
In case if bootloader behave incorrectly and ignore the upgrade state
it can trigger rollback even after successful upgrade.
With working apertis-update-complete service this state is masked
since AUM rewrite the bootcounter file on every successful boot.
However in case if the system is interrupted 3 times in a raw before re-marking update as "successful", the bootloader may start the rollback procedure. For instance in case of sequential power failure or user's interruption.
Added the test emulating failure of the boot process prior starting the mark service after successful upgrade by failing this service. Check if no rollback happens after several boots in a raw.