Separate the Alarm unit tests from testing the Wakelocks

* Simplify the AlarmTestHarnless unit test setup for Wakelocks.
  Now we use wakelock_set_os_callouts() to setup local unit tests and
  to keep local state whether the wakelock is acquired.
  Also, removed unused timer-related setup inside AlarmTestHarnless.

* Add explicit Wakelock unit tests

Change-Id: I08bd8d457fd48ec45a8a591bd69cb08dbaf5ee7a