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: I7d69623c23e2337dde320bcab81f6a0f5c10b289
diff --git a/.zuul.yaml b/.zuul.yaml
index be73dc7..122297a 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -6,10 +6,10 @@
       jobs:
         - barbican-tempest-plugin-simple-crypto
         - barbican-tempest-plugin-simple-crypto-secure-rbac
+        - barbican-tempest-plugin-simple-crypto-xena
         - barbican-tempest-plugin-simple-crypto-wallaby
         - barbican-tempest-plugin-simple-crypto-victoria
         - barbican-tempest-plugin-simple-crypto-ussuri
-        - barbican-tempest-plugin-simple-crypto-train
         - barbican-tempest-plugin-simple-crypto-ipv6-only
         - barbican-tempest-plugin-simple-crypto-castellan-src
         - barbican-tempest-plugin-simple-crypto-cursive
@@ -79,6 +79,11 @@
               enforce_scope: True
 
 - job:
+    name: barbican-tempest-plugin-simple-crypto-xena
+    parent: barbican-tempest-plugin-simple-crypto
+    override-checkout: stable/xena
+
+- job:
     name: barbican-tempest-plugin-simple-crypto-wallaby
     parent: barbican-tempest-plugin-simple-crypto
     override-checkout: stable/wallaby
@@ -96,12 +101,6 @@
     override-checkout: stable/ussuri
 
 - job:
-    name: barbican-tempest-plugin-simple-crypto-train
-    parent: barbican-tempest-plugin-simple-crypto
-    nodeset: openstack-single-node-bionic
-    override-checkout: stable/train
-
-- job:
     name: barbican-tempest-plugin-simple-crypto-ipv6-only
     parent: devstack-tempest-ipv6
     required-projects: *barbican-tempest-reqs