ConfigMotorTest: support Tri frames

[robertlong13]

Support additional motor test information for tri frames. Goes along with this ArduPilot PR, and should probably not be merged until that one is.

This brings the motor test order in line with other frames. Starts with the front-right and works around clockwise, with the addition that "Motor C" controls the tilt servo, which is a little odd, but it's exactly what "Test all in sequence" does, so we should match that.