Parametrize the name of contrail service

This allows to set custom name for contrail service in keystone
catalog.

Change-Id: I75c010de19336a3525e848c414ea78f623ad3870
(cherry picked from commit 5c6e3d6e930a3358ea452ce107d3bd9987a71ea0)
diff --git a/tungsten_tempest_plugin/config.py b/tungsten_tempest_plugin/config.py
index b82299e..d1982ad 100644
--- a/tungsten_tempest_plugin/config.py
+++ b/tungsten_tempest_plugin/config.py
@@ -27,6 +27,9 @@
                          title='SDN service options')
 
 SDNGroup = [
+    cfg.StrOpt('service_name',
+               default='Contrail',
+               help="Name of contrail service in keystone catalog"),
     cfg.StrOpt('endpoint_type',
                default='publicURL',
                choices=['public', 'admin', 'internal',