Fix first battery message on boot

The default battery level was being set to 100 and then displayed
to the user. The correct battery level is received as a broadcast,
so initialize to an invalid value and wait for the first broadcast
to come.

Fixes: 353636704
Test: atest KeyguardIndicationControllerTest
Flag: EXEMPT bugfix
Change-Id: I3c8e85d8d02652253a3895edda28ec4f198e532e