Add post_upgrade_tasks with post_upgrade_steps_playbook output
Add post_upgrade_tasks with post_upgrade_steps_playbook output

This wires up the post_upgrade_tasks tasks to be written as
ansible playbooks like the upgrade/update_tasks. This will
write out a post_upgrade_steps_playbook ansible playbook.

Used in https://review.openstack.org/#/c/489201/ by ODL
and https://review.openstack.org/#/c/505603/ cinder-volume
Q upgrade spec @ Ibde21e6efae3a7d311bee526d63c5692c4e27b28
Related Blueprint: major-upgrade-workflow

Change-Id: Ib6188c91076eabf20d6e358ca247fed802369a7f

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates