GCS_MAVLink: add DO_MOTOR_TEST message
GCS_MAVLink: generate after adding DO_MOTOR_TEST
Copter: add mavlink motor_test
AP_Motors: output_test for individual motors
MotorMatrix: output_test for individual motors
CoaxCopter: output_test for individual motors
TradHeli: output_test for individual motors
SingleCopter: output_test for individual motors
TriCopter: output_test for individual motors
Copter: remove cli motor test