Run slow tests parallely

We started the slow test run serially to avoid
any timeout issue in parallel run. But serial run
takes lot of time and end up with job timeout.

tempest-slow-parallel job exepriment running the slow
tests in parallel and its not so bad. Only 1 timeout
in last 50 run
- https://zuul.opendev.org/t/openstack/builds?job_name=tempest-slow-parallel&skip=0

Let's try running slow tests in parallel in tempest-slow-py3
job itself and if it make situation worst then we can revert
it to run serially.

Change-Id: I1e32e7a07018a05b54515d9e6e6c8bc2fc7fbdff
diff --git a/zuul.d/integrated-gate.yaml b/zuul.d/integrated-gate.yaml
index 70fdc79..9197e64 100644
--- a/zuul.d/integrated-gate.yaml
+++ b/zuul.d/integrated-gate.yaml
@@ -276,7 +276,7 @@
     timeout: 10800
     # This job runs on stable/stein onwards.
     branches: ^(?!stable/(ocata|pike|queens|rocky)).*$
-    vars: &tempest_slow_vars
+    vars:
       tox_envlist: slow-serial
       devstack_localrc:
         CINDER_ENABLED_BACKENDS: lvm:lvmdriver-1,lvm:lvmdriver-2
@@ -301,16 +301,23 @@
     # as swift is ready on py3 from stable/ussuri onwards.
     timeout: 10800
     branches: ^(?!stable/(ocata|pike|queens|rocky|stein|train)).*$
-    vars: *tempest_slow_vars
-
-- job:
-    name: tempest-slow-parallel
-    parent: tempest-slow-py3
-    # This job run slow tests in parallel.
     vars:
       tox_envlist: slow
       devstack_localrc:
-        MYSQL_REDUCE_MEMORY: true
+        CINDER_ENABLED_BACKENDS: lvm:lvmdriver-1,lvm:lvmdriver-2
+        ENABLE_VOLUME_MULTIATTACH: true
+      devstack_plugins:
+        neutron: https://opendev.org/openstack/neutron
+      devstack_services:
+        neutron-placement: true
+        neutron-qos: true
+    group-vars:
+      # NOTE(mriedem): The ENABLE_VOLUME_MULTIATTACH variable is used on both
+      # the controller and subnode prior to Rocky so we have to make sure the
+      # variable is set in both locations.
+      subnode:
+        devstack_localrc:
+          ENABLE_VOLUME_MULTIATTACH: true
 
 - job:
     name: tempest-cinder-v2-api