[WSGI] Move all OVS jobs to use WSGI API module

All the ML2/OVS tempest jobs are now using the WSGI API
module, instead of the eventlet server.

Related-Bug: #2069581
Topic: eventlet-deprecation
Change-Id: I35d700885e6de0f1b92537789ae9819f8b21db0c

zuul.d/tempest-multinode.yaml

@@ -91,6 +91,7 @@
         Q_ML2_TENANT_NETWORK_TYPE: vxlan
         Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch,linuxbridge
         Q_AGENT: openvswitch
+        NEUTRON_DEPLOY_MOD_WSGI: true
       devstack_services:
         br-ex-tcpdump: true
         br-int-flows: true

zuul.d/tempest-singlenode.yaml

@@ -57,6 +57,7 @@
       devstack_localrc:
         Q_AGENT: openvswitch
         Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch
+        NEUTRON_DEPLOY_MOD_WSGI: true
     irrelevant-files: &openvswitch-irrelevant-files
       - ^\.pylintrc$
       - ^test-requirements.txt$