iotests: always use a unique sub-directory per test

iotests: always use a unique sub-directory per test

The current test runner is only safe against parallel execution within
a single instance of the 'check' process, and only if -j is given a
value greater than 2. This prevents running multiple copies of the
'check' process for different test scenarios.

This change switches the output / socket directories to always include
the test name, image format and image protocol. This should allow full
parallelism of all distinct test scenarios. eg running both qcow2 and
raw tests at the same time, or both file and nbd tests at the same
time.

It would be possible to allow for parallelism of the same test scenario
by including the pid, but that would potentially let many directories
accumulate over time on failures, so is not done.

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: <20230303160727.3977246-7-berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230315174331.2959-24-alex.bennee@linaro.org>