Add Keystone role and service test cases

Add two test cases about Keystone role and service:
test_get_role_by_id
test_create_service_without_description

Change-Id: I5c09e82bb9afbb6d1d8a81dfd6e7408b4ffdd58f
diff --git a/tempest/api/identity/admin/test_services.py b/tempest/api/identity/admin/test_services.py
index 459c44c..b0e6cdb 100644
--- a/tempest/api/identity/admin/test_services.py
+++ b/tempest/api/identity/admin/test_services.py
@@ -66,6 +66,20 @@
         self.assertEqual(fetched_service['description'],
                          service_data['description'])
 
+    @attr(type='gate')
+    def test_create_service_without_description(self):
+        # Create a service only with name and type
+        name = data_utils.rand_name('service-')
+        type = data_utils.rand_name('type--')
+        resp, service = self.client.create_service(name, type)
+        self.assertIn('id', service)
+        self.assertTrue('200', resp['status'])
+        self.addCleanup(self._del_service, service['id'])
+        self.assertIn('name', service)
+        self.assertEqual(name, service['name'])
+        self.assertIn('type', service)
+        self.assertEqual(type, service['type'])
+
     @attr(type='smoke')
     def test_list_services(self):
         # Create, List, Verify and Delete Services