Process external_deploy_steps_tasks as a part of config download
mechanism, which will allow services to export Ansible tasks to be
executed on undercloud directly, with full undercloud and overcloud
inventory available.
These tasks can be used to perform complex actions from the
undercloud, such as executing nested installers like kubespray or
ceph-ansible. This should allow deploying overcloud with a single
Ansible playbook, and without creating Ansible->Mistral->Ansible loop.
Implements: blueprint ansible-config-download
Change-Id: I8491540edf78711f3229eabeda22a17cd55e99c8
e47e1dfc26