rhel-osp-director: deploy oc 7.2 from uc 8.0  without netiso: the deployment finishes with error because it's unable to login with heat-admin.

Environment:
openstack-tripleo-0.0.7-1.el7ost.noarch
openstack-tripleo-common-0.0.2-4.el7ost.noarch
openstack-tripleo-puppet-elements-0.0.2-1.el7ost.noarch
openstack-tripleo-image-elements-0.9.7-1.el7ost.noarch
instack-undercloud-2.2.0-1.el7ost.noarch
openstack-tripleo-heat-templates-0.8.6-94.el7ost.noarch

Steps to reproduce:
1. Deploy undercloud 8.0.
2. Get/Load images for 7.2 (Note: BZ #1295912)
3. Downgrade the  openstack-tripleo-heat-templates package to 7.2 version.
4. Run a deployment without network isolation:
 openstack overcloud deploy --templates --control-scale 3 --compute-scale 2    --ntp-server x.x.x.x  --timeout 90 

Result:

Deploying templates in the directory /usr/share/openstack-tripleo-heat-templates

^[[24~PKI initialization in init-keystone is deprecated and will be removed.
Warning: Permanently added '192.168.0.6' (ECDSA) to the list of known hosts.
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
Command '['ssh', '-oStrictHostKeyChecking=no', '-t', '-l', 'heat-admin', u'192.168.0.6', 'sudo', 'keystone-manage', 'pki_setup', '--keystone-user', "$(getent passwd | grep '^keystone' | cut -d: -f1)", '--keystone-group', "$(getent group | grep '^keystone' | cut -d: -f1)"]' returned non-zero exit status 255

Note: it's not possible to login to the overcloud nodes using the heat-admin user.


Expected result:
Successful deployment