Add a test case that schedules an alarm and then, after a delay that
is changed in every iteration, tries to reschedule it to one cycle
later.
This reveals a problem in the current nrf_rtc_timer implementation
that in certain conditions a scheduled timeout may be missed and
its expiration is handled 512 seconds later (when the system timer
overflows).
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
8e8644ba6a