After a Overcloud deployment, /etc/hosts on the undercloud
will be populated with entries for each overcloud node. Since
we use the same tripleo_ansible roles for both the undercloud
and overcloud deployment, the /etc/hosts file on the Director
will be removed by undercloud install / upgrade operations.
This is outlined here:
This change adds the RootStackName to the group_vars,
this is then used by the tripleo_host_entries role in
tripleo-ansible to write host entries per stack.