Refactor shutter action switch case for testing

[evanmayer]

Code coverage odyssey

Start breaking up big function DoShutter() by making one part of it it's own function. Test that function on its own, and replace the block in DoShutter() with the new function.

This is identical to what I have done already for DoLock() for the elevation lock state machine.

[evanmayer]

I'm going to address these things quickly, so another commit incoming.