tests: add tuxrun baseline test to avocado

The TuxRun project (www.tuxrun.org) uses QEMU to run tests on a wide
variety of kernel configurations on wide range of our emulated
platforms. They publish a known good set of images at:

  https://storage.tuxboot.com/

to help with bisecting regressions in either the kernel, firmware or
QEMU itself. The tests are pretty lightweight as they contain just a
kernel with a minimal rootfs which boots a lot faster than most of the
distros. In time they might be persuaded to version their known good
baselines and we can then enable proper checksums.

For a couple of tests we currently skip:

  - mips64, a regression against previous stable release
  - sh4, very unstable with intermittent oops

Total run time: 340s (default) -> 890s (debug)

Overall coverage rate (tested targets + disabled tests):
  lines......: 16.1% (126894 of 789848 lines)
  functions..: 20.6% (15954 of 77489 functions)
  branches...: 9.3% (40727 of 439365 branches)

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230228190653.1602033-11-alex.bennee@linaro.org>

MAINTAINERS

@@ -3766,6 +3766,7 @@ F: scripts/ci/
 F: tests/docker/
 F: tests/vm/
 F: tests/lcitool/
+F: tests/avocado/tuxrun_baselines.py
 F: scripts/archive-source.sh
 F: docs/devel/testing.rst
 W: https://gitlab.com/qemu-project/qemu/pipelines