Don't wake users up with low battery sounds.

Battery sounds will always play when the screen is on, and
then for Settings.Global.LOW_BATTERY_SOUND_TIMEOUT
milliseconds after the screen goes off. After that, low
battery alerts will be pushed out the airlock until the
screen comes back on again.

If battery sounds are suppressed via this mechanism you'll
see a log line like:

	V/PowerUI ( 3161): screen off too long (5779ms, limit
	5000ms): not waking up the user with low battery sound

The default value of LOW_BATTERY_SOUND_TIMEOUT is a settings
provider resource: R.integer.def_low_battery_sound_timeout.

Bug: 10487557
Change-Id: Iddd42038aa630631dc8f1833f20fcc5a0c646681