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>

ipatests/test_integration/base.py

@@ -32,6 +32,8 @@ class IntegrationTest:
     num_replicas = 0
     num_clients = 0
     num_ad_domains = 0
+    num_ad_subdomains = 0
+    num_ad_treedomains = 0
     required_extra_roles = []
     topology = None
     domain_level = None