Add ability to set custom internal dns zone name

Due to internal dns zone name can be custom
we should set it via config option.

Related-prod: PRODX-2967
Change-Id: I92f598c3b3035924e9b90820d0aab0d24dc9fb4e
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index 54dc16e..32ad220 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -115,6 +115,9 @@
                help='Name of ssh user to use with advanced image in tests. '
                     'This is required if advanced image has to be used in '
                     'tests.'),
+    cfg.StrOpt('dns_domain',
+               default='openstackgate.local',
+               help='Name of internal dns zone to use in tests. '),
 ]
 
 # TODO(amuller): Redo configuration options registration as part of the planned
diff --git a/neutron_tempest_plugin/scenario/test_internal_dns.py b/neutron_tempest_plugin/scenario/test_internal_dns.py
index 13ca797..13a0fef 100644
--- a/neutron_tempest_plugin/scenario/test_internal_dns.py
+++ b/neutron_tempest_plugin/scenario/test_internal_dns.py
@@ -72,7 +72,7 @@
             timeout=CONF.validation.ping_timeout * 10)
 
         resolv_conf = ssh_client.exec_command('cat /etc/resolv.conf')
-        self.assertIn('openstackgate.local', resolv_conf)
+        self.assertIn(CONF.dns_domain, resolv_conf)
         self.assertNotIn('starwars', resolv_conf)
 
         self.check_remote_connectivity(ssh_client, 'leia')