tests/functional: Add a function for extracting files from an archive

tests/functional: Add a function for extracting files from an archive

Some Avocado-based tests use the "archive" module from avocado.utils
to extract files from an archive. To be able to use these tests
without Avocado, we have to provide our own function for extracting
files. Fortunately, there is already the tarfile module that will
provide us with this functionality, so let's just add a nice wrapper
function around that.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20240830133841.142644-19-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>