Remove VNC server listen addresses seeting to IPv4 from base job

'devstack' job set the VNC listen addresses 'VNCSERVER_LISTEN' and
'VNCSERVER_PROXYCLIENT_ADDRESS' IPv4 which makes 'devstack-ipv6' job
to either unset those or set for IPv6 values.

Let's remove the setting of those in base job and let lib/nova
set based on configured ip version from job.

'devstack-ipv6' base job will be used to define the IPv6-only jobs
on Tempest and project side gate.

Change-Id: Iea469128b15298aee61245e702d20603c8d376fb
Story: #2005477
Task: #35923

.zuul.yaml

@@ -382,8 +382,6 @@
         SWIFT_HASH: 1234123412341234
         DEBUG_LIBVIRT_COREDUMPS: true
         NOVA_VNC_ENABLED: true
-        VNCSERVER_LISTEN: 0.0.0.0
-        VNCSERVER_PROXYCLIENT_ADDRESS: $HOST_IP
       devstack_local_conf:
         post-config:
           $NEUTRON_CONF:
@@ -479,8 +477,6 @@
           GLANCE_HOSTPORT: "{{ hostvars['controller']['nodepool']['private_ipv4'] }}:9292"
           Q_HOST: "{{ hostvars['controller']['nodepool']['private_ipv4'] }}"
           NOVA_VNC_ENABLED: true
-          VNCSERVER_LISTEN: 0.0.0.0
-          VNCSERVER_PROXYCLIENT_ADDRESS: $HOST_IP
 
 - job:
     name: devstack-ipv6

lib/nova

@@ -601,8 +601,8 @@ function configure_console_compute {
     if is_service_enabled n-novnc || is_service_enabled n-xvnc || [ "$NOVA_VNC_ENABLED" != False ]; then
         # Address on which instance vncservers will listen on compute hosts.
         # For multi-host, this should be the management ip of the compute host.
-        VNCSERVER_LISTEN=${VNCSERVER_LISTEN=$NOVA_SERVICE_LOCAL_HOST}
-        VNCSERVER_PROXYCLIENT_ADDRESS=${VNCSERVER_PROXYCLIENT_ADDRESS=$NOVA_SERVICE_LOCAL_HOST}
+        VNCSERVER_LISTEN=${VNCSERVER_LISTEN:-$NOVA_SERVICE_LOCAL_HOST}
+        VNCSERVER_PROXYCLIENT_ADDRESS=${VNCSERVER_PROXYCLIENT_ADDRESS:-$NOVA_SERVICE_LOCAL_HOST}
         iniset $NOVA_CPU_CONF vnc server_listen "$VNCSERVER_LISTEN"
         iniset $NOVA_CPU_CONF vnc server_proxyclient_address "$VNCSERVER_PROXYCLIENT_ADDRESS"
     else