Initialize values from sticy ACTION_BATTERY_CHANGED

ACTION_BATTERY_CHANGED is sent as a sticky, so classes in SystemUI need
to retrieve the last value as part of initialization.

As there is no API to retrieve this, the only solution is get the last
sticky for now.

Test: atest KeyguardUpdateMonitorTest BatteryControllerTest
Test: manual, restart and observe battery icon
Fixes: 159679049
Change-Id: I9e4ea67a34f9166b863abc8f99b687e542128f8b