Tracking: Implement Configuration Boards

[bradjc]

Configuration boards are specific configurations of the Tock kernel to express specific functionality. This is useful for automated testing and running different configurations of the Tock kernel separately from the default board configurations used by typical boards.

For these to be useful, however, we need to have a suitable set of configuration boards defined in boards/configurations to use when testing or experimenting with certain Tock features. This issue is a tracking issues for which configuration boards we want.

• imix/imix-test-kernel: Run all of the imix kernel tests.