Use has_service in functional test's require_service

Under the covers we want to use has_service, which respects the
overall sdk infrastructure for skipping unnecessary discovery.

Change-Id: Ib47bdc98ffa63ec70b89169574cb03057beecb42

openstack/tests/functional/base.py

@@ -14,7 +14,6 @@ import os
 import openstack.config
 
 from keystoneauth1 import discover
-from keystoneauth1 import exceptions as _exceptions
 from openstack import connection
 from openstack.tests import base
 
@@ -114,8 +113,6 @@ class BaseFunctionalTest(base.TestCase):
             self.assertIsNone(result)
         self.addCleanup(cleanup)
 
-    # TODO(shade) Replace this with call to conn.has_service when we've merged
-    #             the shade methods into Connection.
     def require_service(self, service_type, min_microversion=None, **kwargs):
         """Method to check whether a service exists
 
@@ -128,16 +125,16 @@ class BaseFunctionalTest(base.TestCase):
 
         :returns: True if the service exists, otherwise False.
         """
-        try:
-            data = self.conn.session.get_endpoint_data(
-                service_type=service_type, **kwargs)
-        except _exceptions.EndpointNotFound:
+        if not self.conn.has_service(service_type):
             self.skipTest('Service {service_type} not found in cloud'.format(
                 service_type=service_type))
 
         if not min_microversion:
             return
 
+        data = self.conn.session.get_endpoint_data(
+            service_type=service_type, **kwargs)
+
         if not (data.min_microversion
                 and data.max_microversion
                 and discover.version_between(