Add stable/zed jobs on master gate

As zed is released, we should add its job on master
gate to keep branchless tempest plugins compatible
to stable branch.

Ref: Tempest plugins guide for stable branch testing:
- https://docs.openstack.org/tempest/latest/stable_branch_testing_policy.html

Change-Id: Ie8a57fa9e5ef8bef775b8ab78b7d04bceaf795ed

.zuul.yaml

@@ -8,6 +8,7 @@
       jobs:
         - blazar-tempest-plugin-base
         - blazar-tempest-plugin-ipv6-only
+        - blazar-tempest-plugin-zed
         - blazar-tempest-plugin-yoga
         - blazar-tempest-plugin-xena
         - blazar-tempest-plugin-wallaby
@@ -64,6 +65,12 @@
       - ^doc/.*$
       - ^releasenotes/.*$
 
+- job:
+    name: blazar-tempest-plugin-zed
+    parent: blazar-tempest-plugin-base
+    nodeset: openstack-single-node-focal
+    override-checkout: stable/zed
+
 - job:
     name: blazar-tempest-plugin-yoga
     parent: blazar-tempest-plugin-base