Auto disarm drones on completion

[tessmichi]

In the circle jocs in particular, the drones are overshooting their landing location

[abramowitzK]

One way to do this is to add a hover at the end of the file. They are overshooting because they have non zero velocity when given the land command.

[dennisss]

I'll add to this that we should also ensure that the drone is auto-disarmed upon completion.

Another way to get better landings would be to improve the landing state to compute a slow trajectory down to z=0 and then disarm. PX4 also has well-tested 'land at a point' procedures built in, so we may be able to try to reuse some logic from it.

[dennisss]

Fixed in 'server-refine'