Use py3 version of Tempest Multinode job

tempest-multinode-full is py2 job and not needed to
run on ussuri onwards. Chaning this to its py3
version tempest-multinode-full-py3

Change-Id: Iff271eabcf1a39d6bf6c1fcd55ff2749cab2373f

Author: Ghanshyam Mann

.zuul.yaml

@@ -617,7 +617,7 @@
             irrelevant-files:
               - ^.*\.rst$
               - ^doc/.*$
-        - tempest-multinode-full:
+        - tempest-multinode-full-py3:
             voting: false
             irrelevant-files:
               - ^.*\.rst$