Keyguard: Change fingerprint listening behavior

* This patch affects devices that disable fingerprint
  wake-and-unlock via config_fingerprintWakeAndUnlock,
  and is mainly for fp scanners in the power button
* Don't listen to fingerprints when going to sleep
  to avoid a wakeup being triggered after pressing
  the power button to turn the screen off
* Fixes the following scenario:
 - Turn device on with not registered finger
 - Check time (or something on lock screen)
 - Use registered finger to turn off device,
   and leave finger on the scanner
 - Device screen turns off
 - Device wakes up at home screen

Change-Id: Ia40a6a763420cd716796515ddb9b816232218dc0