Add support for IPv6 tunnel endpoints

Currently, neutron tunnel endpoints must be IPv4 addresses,
i.e. $HOST_IP, although IPv6 endpoints are supported by most
drivers.

Create a TUNNEL_IP_VERSION variable to choose which host IP
to use, either HOST_IP or HOST_IPV6, and configure it in the
OVS and Linuxbridge agent driver files. The default is still
IPv4, but it can be over-ridden by specifying TUNNEL_ENDPOINT_IP
accordingly.

This behaves similar to the SERVICE_IP_VERSION option, which
can either be set to 4 or 6, but not 4+6 - the tunnel overhead
should be consistent on all systems in order not to have MTU
issues.

Must set the ML2 overlay_ip_version config option to match
else agent tunnel sync RPC will not work.

Must set the OVN external_ids:ovn-encap-ip config option to
the correct address.

Updated 'devstack-ipv6-only' job definition and verification role
that will set all services and tunnels to use IPv6 addresses.

Closes-bug: #1619476

Change-Id: I6034278dfc17b55d7863bc4db541bbdaa983a686
diff --git a/lib/neutron b/lib/neutron
index f24ccfb..1b78493 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -230,6 +230,7 @@
             mech_drivers+=",linuxbridge"
         fi
         iniset $NEUTRON_CORE_PLUGIN_CONF ml2 mechanism_drivers $mech_drivers
+        iniset $NEUTRON_CORE_PLUGIN_CONF ml2 overlay_ip_version $TUNNEL_IP_VERSION
 
         iniset $NEUTRON_CORE_PLUGIN_CONF ml2_type_vxlan vni_ranges 1001:2000
         iniset $NEUTRON_CORE_PLUGIN_CONF ml2_type_flat flat_networks $PUBLIC_NETWORK_NAME
@@ -251,10 +252,10 @@
         # Configure the neutron agent
         if [[ $NEUTRON_AGENT == "linuxbridge" ]]; then
             iniset $NEUTRON_CORE_PLUGIN_CONF securitygroup firewall_driver iptables
-            iniset $NEUTRON_CORE_PLUGIN_CONF vxlan local_ip $HOST_IP
+            iniset $NEUTRON_CORE_PLUGIN_CONF vxlan local_ip $TUNNEL_ENDPOINT_IP
         elif [[ $NEUTRON_AGENT == "openvswitch" ]]; then
             iniset $NEUTRON_CORE_PLUGIN_CONF securitygroup firewall_driver openvswitch
-            iniset $NEUTRON_CORE_PLUGIN_CONF ovs local_ip $HOST_IP
+            iniset $NEUTRON_CORE_PLUGIN_CONF ovs local_ip $TUNNEL_ENDPOINT_IP
 
             if [[ "$NEUTRON_DISTRIBUTED_ROUTING" = "True" ]]; then
                 iniset $NEUTRON_CORE_PLUGIN_CONF agent l2_population True