Allow more specific sets for cloud runners

No matter what set we'd have, it would get overriden to "cloud". But, we may want to have a limited test set, and this override would extend it when we don't want that. Thus, use whatever set was originally confiured, and intersect it with the cloud set. If the passed set already has the cloud limitation, the intersection is a noop so we should be all good.

Signed-off-by: Veronika Kabatova vkabatov@redhat.com