Add tempest-slow stable branch jobs on Tempest master gate

To cover the stable branch testing on branchless Tempest
master gate, we test tempest-full version of stable branches.
Let's test the tempest-slow job also for stables branches.

All supported stable branches jobs are added in periodic
stable pipeline. As slow jobs are slow, it will make check pipelines
too heavy if we add all the stable branches slow jobs so
I am adding slow jobs only for the oldest supported stable job
which should cover the tempest master working on most
of the stable.

This will cover the Tempest slow tests stability for stable branches.

Change-Id: Idb8f178fa4fb4b669f3a163d5c5a9517b9d43c9a

zuul.d/project.yaml

@@ -43,6 +43,8 @@
             irrelevant-files: *tempest-irrelevant-files
         - tempest-full-victoria-py3:
             irrelevant-files: *tempest-irrelevant-files
+        - tempest-slow-wallaby:
+            irrelevant-files: *tempest-irrelevant-files
         - tempest-multinode-full-py3:
             irrelevant-files: *tempest-irrelevant-files
         - tempest-tox-plugin-sanity-check:
@@ -167,6 +169,9 @@
         - tempest-full-xena
         - tempest-full-wallaby-py3
         - tempest-full-victoria-py3
+        - tempest-slow-yoga
+        - tempest-slow-xena
+        - tempest-slow-wallaby
     periodic:
       jobs:
         - tempest-all

zuul.d/stable-jobs.yaml

@@ -19,6 +19,21 @@
     parent: tempest-full-py3
     override-checkout: stable/victoria
 
+- job:
+    name: tempest-slow-yoga
+    parent: tempest-slow-py3
+    override-checkout: stable/yoga
+
+- job:
+    name: tempest-slow-xena
+    parent: tempest-slow-py3
+    override-checkout: stable/xena
+
+- job:
+    name: tempest-slow-wallaby
+    parent: tempest-slow-py3
+    override-checkout: stable/wallaby
+
 - job:
     name: tempest-full-py3
     parent: devstack-tempest