Create and append dvr override template for OSP <=14 only
Create and append dvr override template for OSP <=14 only

Dvr override template should be generated only for OSP<=14 otherwise
OSP 17 deployment  with flag --network-dvr yes fails with error:
ValueError: environment has empty section "resource_registry"

Change-Id: I60dee9c4e6bef6aaf1be9df5d94fc8da02eed73f

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared