Remove superfluous role_name arguments

This patch removes the role_name when using openstack_user's :create
action (it gets ignored by the target method).

recipes/identity_registration.rb

@@ -83,7 +83,6 @@ end
 # Register Service User
 openstack_user service_user do
   project_name service_project_name
-  role_name service_role
   password service_pass
   connection_params connection_params
 end