Autotest ONIE

This is beginning of the testing framework for ONIE.

At the moment, it provides just the groundwork:
* Parameter validation
* Dynamic module loading
* Dynamic test definitions
* Basic documentation
That's a possibility.  (i.e. moving the backend choices out to a different file).  Ultimately, we need to be able to run all of these test cases with a variety of tools as not everyone uses the same deployment environment.