3nodes: make it voting

- Remove the job in Ocata (failing and not maintained)
- Make it voting in Pike and Queens.

Having it voting will help to maintain it in good shape and avoid
regressions.

Depends-On: I9829845b83bd43e1d66f6be010369dde8ef47b5a
Change-Id: Ic01518be0c56cf4a41530822917411e77965b73b

zuul.d/multinode-jobs.yaml

@@ -9,6 +9,7 @@
     gate:
       queue: tripleo
       jobs:
+        - tripleo-ci-centos-7-3nodes-multinode
         - tripleo-ci-centos-7-nonha-multinode-oooq
 
 - project-template:
@@ -81,8 +82,7 @@
     post-run: playbooks/tripleo-ci/post.yaml
     timeout: 10800
     nodeset: legacy-centos-7-3-node
-    voting: false
-    branches: ^(?!stable/newton).*$
+    branches: ^(?!stable/(newton|ocata)).*$
     vars:
       toci_jobtype: multinode-2ctlr-featureset032