New major upgrade workflow implementation.

This patch includes the new upgrades workflow to
upgrade to Queens into the tripleo-upgrade role.
A overcloud_upgrade_prepare.sh script will be run
to get the HEAT outputs into Ansible playbooks which
will be run later via as many scripts as roles in
the environment (Controller, Compute, etc...).
In each of these scripts the command to run the
downloaded playbooks is executed.

All containers preparation and downloading tasks
have been moved out of the upgrade playbook, so
it becomes a pre-requisite to have uploaded the
right containers before upgrading using this role.

All this new workflow is based on the steps defined
in [0].

[0] https://review.openstack.org/#/c/535859/

Change-Id: Iae680d97eeef52b9145c290b0b988cb267af3b3d

templates/overcloud_upgrade_converge.sh.j2

@@ -0,0 +1,16 @@
+#!/bin/env bash
+#
+# Run major upgrade converge step on overcloud nodes
+#
+set -euo pipefail
+
+source {{ undercloud_rc }}
+echo "Running major upgrade converge step"
+openstack overcloud upgrade \
+{% if tripleo_upgrade_debug|bool %}
+        --debug \
+{% endif %}
+{% if tripleo_upgrade_skip_validations|bool %}
+        --validation-errors-nonfatal \
+{% endif %}
+        converge 2>&1