Add initial wakefulness state test.

Adds various changes to PowerManagerService to support mocking out
various managers and methods.

Adds a simple goToSleep() API test that verified it went to sleep.

Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/power/PowerManagerServiceTest.java
Change-Id: Iae8d6fcec05c3fc8a48ed5808d6813f1fdd7c7ca