run_once causes failures when not all nodes in batch get promtail

[viq]

According to https://docs.ansible.com/ansible/latest/user_guide/playbooks_strategies.html#running-on-a-single-machine-with-run-once run_once means the task runs only on first node in batch. This fails when this role is included using e.g.

    - role: ansible-role-promtail
      tags: promtail
      when: promtail_enabled

when not all nodes have promtail_enabled: True.