Add stable/xena jobs on master gate

We have stable/xena released so we should add
their job on master gate to keep branchless tempest
plugins compatible to stable branch.

This also removes the stable/train job as that is in EM
state now.

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

Change-Id: Idd1c0ae5211764abb1d3b30735c1986b63005789

.zuul.yaml

@@ -12,10 +12,10 @@
             voting: false
         - cinder-tempest-plugin-cbak-ceph
         - cinder-tempest-plugin-cbak-s3
+        - cinder-tempest-plugin-basic-xena
         - cinder-tempest-plugin-basic-wallaby
         - cinder-tempest-plugin-basic-victoria
         - cinder-tempest-plugin-basic-ussuri
-        - cinder-tempest-plugin-basic-train
         # Set this job to voting once we have some actual tests to run
         - cinder-tempest-plugin-protection-functional:
             voting: false
@@ -26,10 +26,10 @@
         - cinder-tempest-plugin-cbak-ceph
     experimental:
       jobs:
+        - cinder-tempest-plugin-cbak-ceph-xena
         - cinder-tempest-plugin-cbak-ceph-wallaby
         - cinder-tempest-plugin-cbak-ceph-victoria
         - cinder-tempest-plugin-cbak-ceph-ussuri
-        - cinder-tempest-plugin-cbak-ceph-train
 
 - job:
     name: cinder-tempest-plugin-protection-functional
@@ -137,6 +137,12 @@
       devstack_services:
         c-bak: true
 
+- job:
+    name: cinder-tempest-plugin-cbak-ceph-xena
+    parent: cinder-tempest-plugin-cbak-ceph
+    nodeset: openstack-single-node-focal
+    override-checkout: stable/xena
+
 - job:
     name: cinder-tempest-plugin-cbak-ceph-wallaby
     parent: cinder-tempest-plugin-cbak-ceph
@@ -155,12 +161,6 @@
     nodeset: openstack-single-node-bionic
     override-checkout: stable/ussuri
 
-- job:
-    name: cinder-tempest-plugin-cbak-ceph-train
-    parent: cinder-tempest-plugin-cbak-ceph
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/train
-
 # variant for pre-Ussuri branches (no volume revert for Ceph),
 # should this job be used on those branches
 - job:
@@ -236,6 +236,12 @@
       - ^doc/.*$
       - ^releasenotes/.*$
 
+- job:
+    name: cinder-tempest-plugin-basic-xena
+    parent: cinder-tempest-plugin-basic
+    nodeset: openstack-single-node-focal
+    override-checkout: stable/xena
+
 - job:
     name: cinder-tempest-plugin-basic-wallaby
     parent: cinder-tempest-plugin-basic
@@ -253,12 +259,3 @@
     parent: cinder-tempest-plugin-basic
     nodeset: openstack-single-node-bionic
     override-checkout: stable/ussuri
-
-- job:
-    name: cinder-tempest-plugin-basic-train
-    parent: cinder-tempest-plugin-basic
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/train
-    vars:
-      devstack_localrc:
-        USE_PYTHON3: True