Update 'Maintained' stable branch jobs on master gate

We have stable/yoga released and stable/ussuri is in
'Extended Maintenance' state. Current 'Maintained'
stable branches are yoga, xena, wallaby, and victoria.

As per tempest stable branch testing policy[1], adding the
newly released stable/yoga job and remove the EM stable/ussuri
job.

[1] https://docs.openstack.org/tempest/latest/stable_branch_testing_policy.html

Change-Id: I6efd637271247cc33880db6b3ac49243c299cdf9

.zuul.yaml

@@ -7,10 +7,10 @@
       jobs:
         - blazar-tempest-plugin-base
         - blazar-tempest-plugin-ipv6-only
+        - blazar-tempest-plugin-yoga
         - blazar-tempest-plugin-xena
         - blazar-tempest-plugin-wallaby
         - blazar-tempest-plugin-victoria
-        - blazar-tempest-plugin-ussuri
     gate:
       queue: blazar
       jobs:
@@ -65,6 +65,11 @@
       - ^doc/.*$
       - ^releasenotes/.*$
 
+- job:
+    name: blazar-tempest-plugin-yoga
+    parent: blazar-tempest-plugin-base
+    override-checkout: stable/yoga
+
 - job:
     name: blazar-tempest-plugin-xena
     parent: blazar-tempest-plugin-base
@@ -79,9 +84,3 @@
     name: blazar-tempest-plugin-victoria
     parent: blazar-tempest-plugin-base
     override-checkout: stable/victoria
-
-- job:
-    name: blazar-tempest-plugin-ussuri
-    parent: blazar-tempest-plugin-base
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/ussuri