Add IP to HAProxy kind=Optional constraint
Add IP to HAProxy kind=Optional constraint

Without the constraint the VIP could get assigned to a node without
an active haproxy instance, which ultimately means everything stops
working.

kind=Optional allows a VIP to relocate to a healthy haproxy instance
in the event of a failure without tearing down the entire stack in the
process.

Change-Id: I44d44952fb42cf91a2a248250a4063e3034d119e

trozet/opnfv-tht,wyg3958/tripleo-heat-templates,openstack/tripleo-heat-templates,bcrochet/tripleo-heat-templates,bcrochet/tripleo-heat-templates,rdo-management/tripleo-heat-templates,trozet/opnfv-tht,trozet/tripleo-heat-templates,rdo-management/tripleo-heat-templates,wyg3958/tripleo-heat-templates,dprince/tripleo-heat-templates,bcrochet/tripleo-heat-templates,openstack/tripleo-heat-templates,trozet/tripleo-heat-templates,dprince/tripleo-heat-templates,trozet/opnfv-tht