In order to make the deployment more flexible, we should allow for the
ansible hosts to be configurable from the old undercloud/overcloud
concepts. Rather than assume 'undercloud'/'overcloud', we should allow
for these to include the same set of hosts. This change introduces
'deployment_source_hosts' and 'deployment_target_hosts' variables that
can be used to control where the tasks are run on.
Change-Id: I249cc7e179bc1423788aab967c4b2e3f9ffc81d4
Related-Blueprint: all-in-one
3a9c0e8420