Upgraded unit test framework

This creates an upgraded unit test framework. It will automatically run a set of unit tests at boot and report results when you flash the px4fmu-v2_test version of the code. I've currently included the commander and mavlink unit tests as the initial set that is run. I'd be happy to add others (say from systemcmds) that folks think are useful.

Putting this Pull up as a trial balloon mechanism for running/passing unit tests as a requirement prior to Pull acceptance. Hopefully an easier to use mechanism will also encourage more unit test writing. Comments?