doc: update CI & trace sections
Update CI to match current reality, including CTS and 'don't do hardware testing on Docker, really'.
Add separate doc about trace testing, including how to generate traces, how traces are actually run, and the infrastructure side of trace distribution as well.
Since the move to Piglit, this does not reflect reality; using ci-fairy for MinIO access does not respect the cache environment variable. However I think this is fine: the doc describes exactly what labs should do, then when we go back to using cache URLs for trace pulls, they'll swing into action.