Switch tempest multinode job to zuulv3 and python3

Old job name was "legacy-neutron-fwaas-v2-dsvm-tempest-multinode",
new name is "neutron-fwaas-v2-dsvm-tempest-multinode"

Change-Id: Ia717bbac366bbd067e65a3895bb2ffb3aded75b7

.zuul.yaml

@@ -18,7 +18,7 @@
             irrelevant-files:
               - ^(test-|)requirements.txt$
               - ^setup.cfg$
-        - legacy-neutron-fwaas-v2-dsvm-tempest-multinode:
+        - neutron-fwaas-v2-dsvm-tempest-multinode:
             voting: false
     gate:
       jobs:
@@ -62,3 +62,39 @@
       devstack_localrc:
         USE_PYTHON3: true
         NETWORK_API_EXTENSIONS: "agent,binding,dhcp_agent_scheduler,external-net,ext-gw-mode,extra_dhcp_opts,quotas,router,security-group,subnet_allocation,network-ip-availability,auto-allocated-topology,timestamp_core,tag,service-type,rbac-policies,standard-attr-description,pagination,sorting,project-id,fwaas_v2"
+
+- job:
+    name: neutron-fwaas-v2-dsvm-tempest-multinode
+    parent: tempest-multinode-full-py3
+    roles:
+      - zuul: openstack/devstack
+    required-projects:
+      - openstack/devstack-gate
+      - openstack/neutron
+      - openstack/neutron-fwaas
+      - openstack/tempest
+    vars:
+      tox_envlist: all-plugin
+      tempest_test_regex: ^neutron_fwaas\.
+      devstack_plugins:
+        neutron: https://opendev.org/openstack/neutron.git
+        neutron-fwaas: https://opendev.org/openstack/neutron-fwaas.git
+      devstack_services:
+        q-fwaas-v2: true
+      devstack_localrc:
+        NETWORK_API_EXTENSIONS: "agent,binding,dhcp_agent_scheduler,external-net,ext-gw-mode,extra_dhcp_opts,quotas,router,security-group,subnet_allocation,network-ip-availability,auto-allocated-topology,timestamp_core,tag,service-type,rbac-policies,standard-attr-description,pagination,sorting,project-id,fwaas_v2"
+    group-vars:
+      subnode:
+        devstack_services:
+          q-agt: true
+        devstack_localrc:
+          USE_PYTHON3: true
+        devstack_local_conf:
+          post-config:
+            # NOTE(slaweq): We can get rid of this hardcoded absolute path when
+            # devstack-tempest job will be switched to use lib/neutron instead of
+            # lib/neutron-legacy
+            "/$NEUTRON_CORE_PLUGIN_CONF":
+              ovs:
+                tunnel_bridge: br-tun
+                bridge_mappings: public:br-ex