Remove reference opencontrail_control_address

This patch replaces _param:opencontrail_control_address by
_param:neutron_service_host to allow different mapping depending of
your deployment. For example OpenvSwitch support won't use
opencontrail_control_address but something else.
diff --git a/nova/compute/cluster.yml b/nova/compute/cluster.yml
index 7eca116..b27ac38 100644
--- a/nova/compute/cluster.yml
+++ b/nova/compute/cluster.yml
@@ -81,7 +81,7 @@
       network:
         engine: neutron
         region: ${_param:openstack_region}
-        host: ${_param:opencontrail_control_address}
+        host: ${_param:neutron_service_host}
         port: 9696
         user: neutron
         tenant: service