Based on [1], this patch implements changes to
the playbook which executes the nova deployment
in a play per host group, serialised to ensure
that:
1. The services are changed in the right order.
2. The API services remain available at all times during
an upgrade.
3. If services are sharing a host/container then the
role execution will not execute twice on the same
host.
[1] https://docs.openstack.org/developer/nova/upgrade.html
Depends-On: I08e5a7f0ce526b11aa52c35ee29c458954a5f22d
Change-Id: I3173962a35b716fd9b0b2a526420fcc5d844befa
4cef8b6b20