Add tests to cover policy_dscp_marking_rule

This patch set adds tests to cover the policy_dscp_marking_rule API [0].
Test creates, showes, updates and deletes policy_dscp_marking_rule.
Part of "Increase Neutron RBAC Coverage" initiative [1]

[0] https://developer.openstack.org/api-ref/network/v2/index.html#qos-dscp-marking-rules
[1] https://storyboard.openstack.org/#!/story/2002641

Change-Id: I34e6276784828c518513c5fe9caf1eee1669658a
Story: 2002641
Task: 22320
diff --git a/.zuul.yaml b/.zuul.yaml
index 5701eb4..2e29ccf 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -151,6 +151,7 @@
         tempest: true
         neutron: true
         neutron-segments: true
+        neutron-qos: true
 
 - job:
     name: patrole-plugin-member