Fix status bar flickering

The keyguard status bar would be visible momentarily while the keyguard
is fading out. Let's keep it hidden until the keyguard is gone.

Test: reach, auth, press power, look at status bar: gone
Test: reach, press power, look at status bar: gone
Test: reboot, reach, press power, look at status bar: visible
Test: reach, press power, wait for auth filure, look at status bar: visible
Test: reach, pull down, wait for auth filure, look at status bar: visible
Fixes: 140259100
Change-Id: I0aa705107e11e3ad8182ac8d5b6104c9f86754be