fix sanity test to use active user when running 'rpm-ostree status'

[miabbott]

rpm-ostree has changed to only allow active users to run rpm-ostree status

We need to update the role/test accordingly.

See this comment (and the linked commits) for more detail

coreos/rpm-ostree#898 (comment)

[miabbott]

I think we can do this with a combination of adduser on the host and the become_user Ansible directive.

http://docs.ansible.com/ansible/latest/become.html

[miabbott]

Yeah, we should rework the command_user_verify role to use that ⬆️