Don't consider the boot completed until the animation is over.

This fixes a problem where the screen times out shortly after
boot before the user has had a chance to interact with the device.
Now we wait until the boot animation has completed then set
boot completed, poke user activity and start the countdown.

Bug: 7316397
Change-Id: Ie5a0b1012d265e655d33cc8fba49ca349f48f1de