Update opacity of LightRevealScrim

So when the motion sense 'reach' sensor is triggered,
the wallpaper is visible behind a semi-transparent
LightRevealScrim.

BehindScrim is no longer used for its opaque black background on AOD.
Instead, we rely on the light reveal scrim. Update tests to reflect
this

Test: manual, atest ScrimControllerTest
Fixes: 187670193
Change-Id: I33cf27e12fa74aea80f3e2363c49253f1632baed