utils_test: Handle transition global_config -> settings

Autotest upstream renamed one particular API:

global_config -> settings

In order to make it cleaner. As we are still in the process
to make autotest 0.15, let's handle gracefully both
libraries installed in the system. This way, we can resume
regression testing for the next branches of both projects.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>