Implement propeller test functionality

[tobbeanton]

Vibration of the propeller or possible motor/bent axis can effect flight performance. By using the accelerometer it should be possible to implement an automated test to measure this.

[tobbeanton]

A initial implementation has been made and it works like this.

• To run the propeller test the parameter health.startPropTest should be set to 1. This can be done using the cfclient or using the python lib parameter framework e.g. cf.param.set_value('health.startPropTest', '1'). Setting it again will run another new test.
• The test will then run by spinning each propeller after another to check the vibration. If a propeller is found to be over the limit (set in config.h as PROPELLER_BALANCE_TEST_THRESHOLD) the failed propeller will make three short beeps and a sound so it can be identified.
• In the console in the cfclient information of the test will be printed and also if any propeller failed.
• After a test has run it might be wise to restart the CF2.

[benkuper]

It works very well, still have to see how better the flights are, but command is working and it's very reassuring !
Quick note : the parameter to set is health.startPropTest and not runPropTest

[tobbeanton]

Updated the instructions health.startPropTest. Thanks Ben!