Make v3 update_role use **kwargs & doc string

As we discussed on
http://lists.openstack.org/pipermail/openstack-dev/2015-July/068864.html
All http POST/PUT methods need to contain **kwargs as their arguments.

This patch makes update_role of v3 identity_client use **kwargs.
Also update doc string for the same.

Partially implements blueprint consistent-service-method-names

Change-Id: Ic30ce16d5240e597b5abab1590fbfa251321f2b1
diff --git a/tempest/api/identity/admin/v3/test_roles.py b/tempest/api/identity/admin/v3/test_roles.py
index 3be2643..f1edf9b 100644
--- a/tempest/api/identity/admin/v3/test_roles.py
+++ b/tempest/api/identity/admin/v3/test_roles.py
@@ -75,7 +75,8 @@
         self.assertEqual(role['name'], r_name)
 
         new_name = data_utils.rand_name('NewRole')
-        updated_role = self.client.update_role(new_name, role['id'])['role']
+        updated_role = self.client.update_role(role['id'],
+                                               name=new_name)['role']
         self.assertIn('name', updated_role)
         self.assertIn('id', updated_role)
         self.assertIn('links', updated_role)
diff --git a/tempest/services/identity/v3/json/identity_client.py b/tempest/services/identity/v3/json/identity_client.py
index bbd8804..1dea151 100644
--- a/tempest/services/identity/v3/json/identity_client.py
+++ b/tempest/services/identity/v3/json/identity_client.py
@@ -205,12 +205,13 @@
         body = json.loads(body)
         return service_client.ResponseBody(resp, body)
 
-    def update_role(self, name, role_id):
-        """Create a Role."""
-        post_body = {
-            'name': name
-        }
-        post_body = json.dumps({'role': post_body})
+    def update_role(self, role_id, **kwargs):
+        """Update a Role.
+
+        Available params: see http://developer.openstack.org/
+                          api-ref-identity-v3.html#updateRole
+        """
+        post_body = json.dumps({'role': kwargs})
         resp, body = self.patch('roles/%s' % str(role_id), post_body)
         self.expected_success(200, resp.status)
         body = json.loads(body)