Copter: test if autotune's test-gains feature works

[rmackay9]

It is possible/likely that as part of moving Copter's AutoTune feature to a library that the ability for the user to test the gains has been lost.

It's somewhat documented on the wiki but this should work:

• user flies the vehicle in AutoTune and it successfully completes
• user lands and switches to another mode (but does not disarm) and then switches back to AutoTune
• vehicle should now be using the new gains so the user can test them
• if the user switches out of AutoTune (i.e. to AltHold) it should go back to the original gains

@lthall is this your understanding of how a user should be able to test the AutoTune gains? Is this perhaps too complicated?

[lthall]

ArduCopter-3.2.1 Low did nothing Mid loads the normal gains High loads the tuned gains if autotune is finished.

I think we can do much better than this now though.