Add first VLAN Transparency tests

These tests are only executed if the vlan-transparent extension is installed
Advanced images are required because VLANs need to be configured on
the servers, which is not possible with cirros
Connectivity between servers via VLAN interface is verified

Functions add_route, delete_route and delete_address are added to class
IPCommand because they are needed for some VLAN Transparency downstream tests

Change-Id: I448203ead31f17a51f756667f6b3fc8e70a77ed2
diff --git a/zuul.d/ussuri_jobs.yaml b/zuul.d/ussuri_jobs.yaml
index b71a460..9cc0621 100644
--- a/zuul.d/ussuri_jobs.yaml
+++ b/zuul.d/ussuri_jobs.yaml
@@ -163,6 +163,7 @@
         OVN_BUILD_MODULES: True
         # TODO(skaplons): v2.13.1 is incompatible with kernel 4.15.0-118, sticking to commit hash until new v2.13 tag is created
         OVS_BRANCH: 0047ca3a0290f1ef954f2c76b31477cf4b9755f5
+        OVN_BRANCH: "v20.03.0"
 
 - job:
     name: neutron-tempest-plugin-dvr-multinode-scenario-ussuri