Add tempest-multinode-full-py3 job definition

This job is based on tempest-multinode-full job but it
runs on Python 3.

Change-Id: Id387452730133d687ee13e3a38c6bc392a4bba3e

.zuul.yaml

@@ -222,6 +222,13 @@
           LIVE_MIGRATION_AVAILABLE: true
           USE_BLOCK_MIGRATION_FOR_LIVE_MIGRATION: true
 
+- job:
+    name: tempest-multinode-full-py3
+    parent: tempest-multinode-full
+    vars:
+      devstack_localrc:
+        USE_PYTHON3: true
+
 - nodeset:
     name: openstack-bionic-node
     nodes:
@@ -500,6 +507,8 @@
             irrelevant-files: *tempest-irrelevant-files
         - tempest-multinode-full:
             irrelevant-files: *tempest-irrelevant-files
+        - tempest-multinode-full-py3:
+            irrelevant-files: *tempest-irrelevant-files
         - tempest-tox-plugin-sanity-check:
             irrelevant-files:
               - ^(test-|)requirements.txt$