Description of problem:
Overcloud deployment fails with ailed to validate nested template: Property error: resources[8].properties: Property KeystoneFernetKey1 not assigned"

Version-Release number of selected component (if applicable):
python-tripleoclient-6.0.0-0.20161028122504.95bbccf.el7ost.noarch
openstack-tripleo-common-6.0.0-0.20161021193416.2af623f.el7ost.noarch
openstack-tripleo-heat-templates-6.0.0-0.20161220000655.58d711e.el7ost.noarch

How reproducible:
100%

Steps to Reproduce:
1. Deploy overcloud:
source ~/stackrc
export THT=/usr/share/openstack-tripleo-heat-templates/

openstack overcloud deploy --templates $THT \
-r ~/openstack_deployment/roles/roles_data.yaml \
-e $THT/environments/puppet-pacemaker.yaml \
-e $THT/environments/network-isolation.yaml \
-e $THT/environments/network-management.yaml \
-e $THT/environments/storage-environment.yaml \
-e ~/openstack_deployment/environments/nodes.yaml \
-e ~/openstack_deployment/environments/network-environment.yaml \
-e ~/openstack_deployment/environments/disk-layout.yaml \
-e ~/openstack_deployment/environments/neutron-settings.yaml

Actual results:
Deployment fails fast with the following error:
 u'message': u"Failed to run action [action_ex_id=3974d6f1-862e-4064-b7e1-5c1df8f03835, action_cls='<class 'mistral.actions.action_factory.DeployStackAction'>', attributes='{}', params='{u'container': u'overcloud', u'timeout': 240}']\n ERROR: Failed to validate: : resources.ServiceApiServiceChain: : Failed to validate nested template: Property error: resources[8].properties: Property KeystoneFernetKey1 not assigned",
 u'status': u'FAILED'}


Expected results:
Deployment proceeds.

Additional info:
Workaround: pass the following parameters in an environment file:
parameter_defaults:
  KeystoneFernetKey1: azerty
  KeystoneFernetKey0: azerty