Fix power manager issues.

1. If a new brightness animation is started while an unrelated one is
ongoing complete the old animation immediately. Unrelated means that
the old and new animations apply to different devices (button,
keyboard, or screen).

2. Do not interpret turning off the keyboard or button lights as
turning off the screen in isScreenTurningOffLocked().

Fixes bug 6519847.

Change-Id: I53a20951036bcdb793daeff84a9ebeed44be01fc