Make shutdown led pattern have priority over powerup pattern

If bootup must be cancelled before it finishes (for example due to battery
or thermal policy) and shutdown is started, we can have a situation where
both powerup and shutdown led patterns are active simultaenously. After the
fix we will show the shutdown led pattern in cases like this.

[mce] Make shutdown led pattern have priority over powerup pattern. Fixes JB#17671
Merge pull request #142 from spiiroin/led_priorities

Make shutdown led pattern have priority over powerup pattern