Increase tempest test timeout to 30 mintues

test_network_policy_add_remove_pod is often not finishing in 20 minutes
in the gate, effectively timing out the tempest default timeout. This
commit increases the timeout to 30 minutes to avoid that.

Change-Id: I3bbac8e90553be9424fa0ecdb4c05e096da8f2d7

.zuul.d/base.yaml

@@ -34,6 +34,7 @@
       # Default swap size got shrinked to 1 GB, it's way too small for us.
       configure_swap_size: 8192
       tempest_test_regex: '^(kuryr_tempest_plugin.tests.)'
+      tempest_test_timeout: 1800
       tox_envlist: 'all'
       devstack_localrc:
         KURYR_K8S_API_PORT: 8080