Prevent light.turn_on of light that was just turned off

[basnijholt]

Closes #726

This was a rare condition that showed up when the update that happens at interval occurred at the same moment as light.turn_off was called. In that case this happens in this order:

1. someone calls light.turn_off, but light_state=off has not been registered
2. AL starts regular update
3. HA registers light as off
4. AL makes an update and sets the colors/brightness to the state it thinks it should have (which turns on the light again).