Bug 991641 - [v1.3] Backport test_clock_set_alarm.py to v1.3

In this pull I merged  test_clock_set_alarm_repeat.py, test_clock_set_alarm_sound.py and test_clock_set_alarm_snooze.py. I also modified some methods and tests to match the ones from master. I ran all the clock tests locally and they passed. But I will also open an adhoc run too see how tests behave.