Use the renamed vnc options

As the following commit has renamed the two vnc options; let's
use the new options in devstack:
https://review.openstack.org/#/c/498387/

Change-Id: Id125666814ea9bb8a22b579aee0f6bc1c65ade80
diff --git a/lib/nova_plugins/hypervisor-libvirt b/lib/nova_plugins/hypervisor-libvirt
index 0c08a0f..3d676b9 100644
--- a/lib/nova_plugins/hypervisor-libvirt
+++ b/lib/nova_plugins/hypervisor-libvirt
@@ -71,8 +71,8 @@
         iniset $NOVA_CONF libvirt connection_uri "parallels+unix:///system"
         iniset $NOVA_CONF libvirt images_type "ploop"
         iniset $NOVA_CONF DEFAULT force_raw_images  "False"
-        iniset $NOVA_CONF vnc vncserver_proxyclient_address  $HOST_IP
-        iniset $NOVA_CONF vnc vncserver_listen $HOST_IP
+        iniset $NOVA_CONF vnc server_proxyclient_address  $HOST_IP
+        iniset $NOVA_CONF vnc server_listen $HOST_IP
         iniset $NOVA_CONF vnc keymap
     elif [[ "$NOVA_BACKEND" == "LVM" ]]; then
         iniset $NOVA_CONF libvirt images_type "lvm"