Fix 3391330: Use BATTERY_STATUS_FULL as "Charged" state [DO NOT MERGE]

Some devices that use LiPo batteries do not charge them to 100%
as a safety margin and to preserve battery longevity.  This change
allows KeyguardUpdateMonitor to determine when the battery state should be
reported as "Charged", provided the device sets BATTERY_STATUS_FULL in
that case.

Change-Id: Iac6cb78e24f9a696017459cc773c38ef7fe7779f