Fix tempest-slow-py3 job for < stable/xena

tempest-slow-py3 job started using the new tox env
'slow' which is not present in old tempest used in
< stable/xena. This commit preapre a separate job
definiton for stable testing which use the old tox
env.

Closes-Bug: #2027817
Change-Id: Ibe603004ef1a8694a9c6b354b85189273787b3f3
diff --git a/zuul.d/integrated-gate.yaml b/zuul.d/integrated-gate.yaml
index 9197e64..0901788 100644
--- a/zuul.d/integrated-gate.yaml
+++ b/zuul.d/integrated-gate.yaml
@@ -300,7 +300,10 @@
     # This job version is with swift enabled on py3
     # as swift is ready on py3 from stable/ussuri onwards.
     timeout: 10800
-    branches: ^(?!stable/(ocata|pike|queens|rocky|stein|train)).*$
+    # As the 'slow' tox env which is not available in old tempest used
+    # till stable/wallaby, this job definition is only for stable/xena
+    # onwards and separate job definition until stable/wallaby
+    branches: ^(?!stable/(ocata|pike|queens|rocky|stein|train|ussuri|victoria|wallaby)).*$
     vars:
       tox_envlist: slow
       devstack_localrc: