fix dns_domain option call

followup change-id I92f598c3b3035924e9b90820d0aab0d24dc9fb4e

Related-prod: PRODX-2967
Change-Id: I60830504e281ff551afed18bec017b2873101bab
diff --git a/neutron_tempest_plugin/scenario/test_internal_dns.py b/neutron_tempest_plugin/scenario/test_internal_dns.py
index 13a0fef..d30639b 100644
--- a/neutron_tempest_plugin/scenario/test_internal_dns.py
+++ b/neutron_tempest_plugin/scenario/test_internal_dns.py
@@ -72,8 +72,9 @@
             timeout=CONF.validation.ping_timeout * 10)
 
         resolv_conf = ssh_client.exec_command('cat /etc/resolv.conf')
-        self.assertIn(CONF.dns_domain, resolv_conf)
+        self.assertIn(CONF.neutron_plugin_options.dns_domain, resolv_conf)
         self.assertNotIn('starwars', resolv_conf)
 
         self.check_remote_connectivity(ssh_client, 'leia')
-        self.check_remote_connectivity(ssh_client, 'leia.openstackgate.local')
+        self.check_remote_connectivity(
+            ssh_client, 'leia.' + CONF.neutron_plugin_options.dns_domain)