ipatests: adapt test_trust.py for changes in multihost fixture
AD hosts can now be extracted from list in respective class attributes and host
domain names -- from properties provided by multihost plugin (host.domain.name).
Also removed conditional skips of tests when test configuration contains only
part of required AD machines as this feature never worked:
multihost plugin removes all machines from config which are not explicitly
requested.
Related to https://pagure.io/freeipa/issue/7889
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>