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 b/lib/nova
index 1112f29..ea0d2f7 100644
--- a/lib/nova
+++ b/lib/nova
@@ -520,8 +520,8 @@
         # For multi-host, this should be the management ip of the compute host.
         VNCSERVER_LISTEN=${VNCSERVER_LISTEN=$NOVA_SERVICE_LOCAL_HOST}
         VNCSERVER_PROXYCLIENT_ADDRESS=${VNCSERVER_PROXYCLIENT_ADDRESS=$NOVA_SERVICE_LOCAL_HOST}
-        iniset $NOVA_CONF vnc vncserver_listen "$VNCSERVER_LISTEN"
-        iniset $NOVA_CONF vnc vncserver_proxyclient_address "$VNCSERVER_PROXYCLIENT_ADDRESS"
+        iniset $NOVA_CONF vnc server_listen "$VNCSERVER_LISTEN"
+        iniset $NOVA_CONF vnc server_proxyclient_address "$VNCSERVER_PROXYCLIENT_ADDRESS"
         iniset $NOVA_CONF vnc novncproxy_host "$NOVA_SERVICE_LISTEN_ADDRESS"
         iniset $NOVA_CONF vnc xvpvncproxy_host "$NOVA_SERVICE_LISTEN_ADDRESS"
     else