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
(cherry picked from commit b866ad3d34fbe7f89b120359763fcca4281173bb)
(cherry picked from commit 7dcf4c42cf93f44fb362ec081a4088b36acff087)
(cherry picked from commit e36a2d3ee4518282eee844b74acdd379e945c815)
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index a40fb0d..766582b 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -147,6 +147,9 @@
     cfg.BoolOpt('bgp_schedule_speakers_to_agents',
                 default=False,
                 help='Schedule BGP speakers to agents explicitly.'),
+    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 692bb70..9a42e62 100644
--- a/neutron_tempest_plugin/scenario/test_internal_dns.py
+++ b/neutron_tempest_plugin/scenario/test_internal_dns.py
@@ -129,13 +129,16 @@
             servers=[self.server, leia])
 
         resolv_conf = ssh_client.exec_command('cat /etc/resolv.conf')
-        self.assertIn('openstackgate.local', resolv_conf)
+        self.assertIn(CONF.neutron_plugin_options.dns_domain, resolv_conf)
         self.assertNotIn('starwars', resolv_conf)
 
         self.check_remote_connectivity(ssh_client, 'leia',
                                        servers=[self.server, leia])
-        self.check_remote_connectivity(ssh_client, 'leia.openstackgate.local',
-                                       servers=[self.server, leia])
+        self.check_remote_connectivity(
+            ssh_client,
+            'leia.' + CONF.neutron_plugin_options.dns_domain,
+            servers=[self.server, leia]
+        )
 
     @utils.requires_ext(extension="dns-integration", service="network")
     @decorators.idempotent_id('db5e612f-f17f-4974-b5f1-9fe89f4a6fc9')