Migrate Tron logs for power to multimetric format.

As best I can tell, values 3 & 4 (theoretically totalTouchDownTime &
touchCycles, per PowerScreenStateParser) were always set to 0; I
have not migrated these fields.

Test: Manually checked old vs new logs side by side in event log.

Change-Id: Ifbc32cd2006cc94327301bae7541ca25b14f0a40