Makes "segmentation_id" configurable

We should add the segmentation_id as tempest option,
so that it can be changed to match the deployment if needed.

Change-Id: I42bea9217462226e8650e55997449e1cc05f085c
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index 4fad1fa..a6d5c09 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -242,6 +242,17 @@
 CONF.register_group(taas_group)
 CONF.register_opts(TaasGroup, group="taas")
 
+# DNS Integration with an External Service
+DnsFeatureGroup = [
+    cfg.IntOpt(
+        'segmentation_id', default=12345,
+        help="For network types VLAN, GRE, VXLAN or GENEVE, the segmentation"
+             " ID must be outside the ranges assigned to project networks."),
+]
+dns_feature_group = cfg.OptGroup(
+    name='designate_feature_enabled', title='Enabled Designate Features')
+CONF.register_group(dns_feature_group)
+CONF.register_opts(DnsFeatureGroup, group="designate_feature_enabled")
 
 config_opts_translator = {
     'project_network_cidr': 'tenant_network_cidr',