Running regression tests on hardware

[wkz]

While the existing regression testing done in QEMU is great, we also want to run the same tests on real hardware with switch ASICs. In this scenario we want the reporting of results to be asynchronous with respect to the regular Action that builds and runs tests.

Broadly, we want to:

• Keep the existing build+test pipeline in place
• Hardware specific test rigs would then
  1. Pick up new images built by existing pipeline (by simply polling, unless we can come up with something more fancy)
  2. Run regression test suite (might be the standard one, might include extra tests)
  3. Report the results to the commit via the status API