Ansible Tower inventory role requires 'variables' parameter

[pabrahamsson]

The README for manage-inventories states that ansible_tower.inventories.variables is not a required variable. But it is used explicitly in the inventory.j2 template.

{
    "name": "{{ inventory.name }}",
    "description": "{{ inventory.description | default('') }}",
    "organization": {{ org_id }},
    "variables": "{{ inventory.variables }}"
}