iotests: register each I/O test separately with meson

iotests: register each I/O test separately with meson

Currently meson registers a single test that invokes an entire group of
I/O tests, hiding the test granularity from meson. There are various
downsides of doing this

 * You cannot ask 'meson test' to invoke a single I/O test
 * The meson test timeout can't be applied to the individual
   tests
 * Meson only gets a pass/fail for the overall I/O test group
   not individual tests
 * If a CI job gets killed by the GitLab timeout, we don't
   get visibility into how far through the I/O tests
   execution got.

This switches meson to perform test discovery by invoking 'check' in
dry-run mode. It then registers one meson test case for each I/O
test. Parallel execution remains disabled since the I/O tests do not
use self contained execution environments and thus conflict with
each other.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Hanna Czenczek <hreitz@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230303160727.3977246-8-berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230315174331.2959-25-alex.bennee@linaro.org>