Add shutdown reason as extra when triggering ACTION_REQUEST_SHUTDOWN.

When BatteryService triggers ACTION_REQUEST_SHUTDOWN intent, add the reason
for shutdown as extra to indicate low battery or critical battery
thermal state.

Bug: 63736262
Test: 1/ adb shell cmd battery unplug && adb shell cmd battery set level 0
      2/ Power on the device
      3/ Verify sys.boot.reason == shutdown,battery
Test: 1/ adb shell cmd battery set temp 700
      2/ Power on the device
      3/ Verify sys.boot.reason == shutdown,thermal,battery

Change-Id: If20a36ef53f8bcbfae4114df08f741ec1dcd7df9