KCIDB: Test schema enhancements

Hello everyone (potentially) involved with sending data to KCIDB,

We've been working hard at KernelCI to bring you a bunch of exciting changes,
to be presented at LPC in September, and in our news channels.

Meanwhile I'd like to propose two small, but potentially very useful changes
to the I/O schema for tests:

* Supporting non-binary outputs beyond PASS/FAIL -
  integers/floats/booleans/strings/etc. - useful for performance tests.

* Supporting recording `compatible` values from the top of the device tree
  inside the test environment, for machines which use them - useful for
  correlating test results by hardware.

Here's the corresponding schema PR:

    https://github.com/kernelci/kcidb-io/pull/85

I'll follow up with a separate message for each of the changes, going over the
details and the rationale.

Feel free to reply to this or the other messages and leave comments in the PR!

Nick