Unchecked battery saver switch once it's 1st launch

 - Add low battery warning ack check to onSwitchChanged(), reset the
   switch to off once it's 1st time launch, the switch should be enable
   by battery saver change event at 1st instead of enable directly, will
   not check this state anymore after 1st launch

Bug: 227725656
Test: make RunSettingsRoboTests
Change-Id: I79f502f567fae5dd10166d8b24fd50d59c261001