Add ansible_group_vars to config download
Add ansible_group_vars to config download

This change adds support for Ansible vars to be provided via a new
interface in tht and consumed by config-download. Vars are written
under $config-download-dir/group_vars/ where they can be accessed
by ansible commands.

Part of blueprint ansible-tasks-to-role.
Depends-On: Ib70e7dda13b4a3ed30af88906ba42c25cdc93038

Change-Id: I1c8b9530506ee8308c6d369d5587f8b45a3e5ca4
Co-Authored-By: Alex Schultz <6963656cd5f1036a86f38d6c01e67c3f63074c58@redhat.com>

openstack/tripleo-common,openstack/tripleo-common