gitlab: show testlog.txt contents when cirrus/custom-runner jobs fail

gitlab: show testlog.txt contents when cirrus/custom-runner jobs fail

When tests fail meson just displays a summary and tells you to look at
the testlog.txt file for details. The native jobs on shared runners
publish testlog.txt as an artifact. For the Cirrus jobs and custom
runner jobs this is not currently possible. The best we can do is cat
the log contents on failure, to give maintainers a fighting chance
of diagnosing the problem.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220722130431.2319019-3-berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220725140520.515340-3-alex.bennee@linaro.org>