Skip `remote_user` (or `user`) in Ansible playbook

ansible-playbook does not pick up 'ssh user' command line argument **when `remote_user` (or `user`) is defined in given playbook file**. 

In order to ensure that Vagrant user is used, `ansible_ssh_user` needs to be added to the inventory file (or exported as extra variable).

The main question is now: Should Vagrant allow this override, or not? As illustrated here, current behavior can be confusing. On the other hand people using this `remote_user` may disagree that Vagrant silently skips this playbook requirement...