bug: motor test triggering on page load

[goasChris]

Bug description

When opening pwm outputs in vehicle setup while the robot is armed, we get a flood of critical status_texts.

Steps to reproduce

1. Run rover firmware
2. Have the robot armed
3. Observe status_text mavlink messages
4. go to vehicle setup/pwm outputs: /vehicle/setup/pwm_outputs
5. Observe flood of critical messages

Primary pain point(s)

A flood of critical messages is not great for our monitoring tools. I suspect we won't be able to actually run the motor tests (we don't use it, but still).

Additional context

Our autopilot firmware has some modifications, so its not impossible that this is not reproducible (sorry about that) with stock.

I suspect I might be hitting this piece of the new code, and its generating some critical status_text messages:
#3113

or perhaps:
#3122

MOTOR TEST: INVALID MOTOR (3) (and 4)

https://github.com/ArduPilot/ardupilot/blame/master/Rover/motor_test.cpp#L85

This might be our own doing, just wondering what the auto-set we are enabling. I didnt even run the motor test, I just opened the page vehicle/setup/pwm_outputs, and was flooded.

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.