GCS_MAVLink: add DO_MOTOR_TEST message
GCS_MAVLink: generate after adding DO_MOTOR_TEST
Copter: add mavlink motor_test

Based on original work by Nils Hogberg
AP_Motors: output_test for individual motors

Modified and integrated by Randy Mackay
MotorMatrix: output_test for individual motors

Based on original work by Nils Hogberg
CoaxCopter: output_test for individual motors

Based on original work by Nils Hogberg
TradHeli: output_test for individual motors

Based on original work by Nils Hogberg
SingleCopter: output_test for individual motors

Based on original work by Nils Hogberg
TriCopter: output_test for individual motors

Based on original work by Nils Hogberg
Copter: remove cli motor test