Make identity v3 roles_client use **kwargs

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 identity v3 roles_client use **kwargs.

Also rename some method to match the consistency across v2 and v3
service client

Partially implements blueprint consistent-service-method-names

Change-Id: I2737c3a9c448c16440d2707b31fa3f99876d25a0
diff --git a/tempest/api/identity/admin/v3/test_tokens.py b/tempest/api/identity/admin/v3/test_tokens.py
index fcf4772..8706cf7 100644
--- a/tempest/api/identity/admin/v3/test_tokens.py
+++ b/tempest/api/identity/admin/v3/test_tokens.py
@@ -83,11 +83,11 @@
         self.addCleanup(self.roles_client.delete_role, role['id'])
 
         # Grant the user the role on both projects.
-        self.roles_client.assign_user_role_on_project(project1['id'],
+        self.roles_client.create_user_role_on_project(project1['id'],
                                                       user['id'],
                                                       role['id'])
 
-        self.roles_client.assign_user_role_on_project(project2['id'],
+        self.roles_client.create_user_role_on_project(project2['id'],
                                                       user['id'],
                                                       role['id'])