Use py2.7 compatible kuryr-tempest-plugin for stable/rocky

stable/rocky python2.7 jobs need to use the py2.7
compatible version of kuryr-tempest-plugin which is
0.5.0. Tempest is already using old Tempest for stable/rocky
- c431116ceb/stackrc (L316)

Change-Id: I4a968a74ac99f31ccc6a0f6a2d74df607c745dc8

.zuul.d/base.yaml

@@ -21,7 +21,8 @@
       - openstack/devstack-plugin-container
       - openstack/kuryr
       - openstack/kuryr-kubernetes
-      - openstack/kuryr-tempest-plugin
+      - name: openstack/kuryr-tempest-plugin
+        override-checkout: 0.5.0
       - openstack/neutron-lbaas
       - openstack/tempest
     post-run: playbooks/copy-k8s-logs.yaml