Update overcloud template description and Count constraints
Update overcloud template description and Count constraints

Currently there's a vague list of services in the description, so instead
describe the roles supported for deployment, and encode the minimum allowed
of one Controller/Compute with zero Storage nodes in the parameter constraints.

Change-Id: Ib4917843f3e4770f0260db72719ed6af0ee8dc13

dprince/tripleo-heat-templates,dprince/tripleo-heat-templates,trozet/opnfv-tht,trozet/opnfv-tht,bcrochet/tripleo-heat-templates,openstack/tripleo-heat-templates,openstack/tripleo-heat-templates,trozet/opnfv-tht,bcrochet/tripleo-heat-templates,trozet/tripleo-heat-templates,trozet/tripleo-heat-templates,bcrochet/tripleo-heat-templates