Temporarly mark 3node job as non-voting

There's a bug in TestNetworkBasicOps tempest job that prevent patches to
land, and it's impacting 3node job, and the fix for this is creating a
circular dependence.

Change-Id: I339a0fef6b73ba2404d8797b8767fca9cf919664
Related-Bug: 1757556

zuul.d/multinode-jobs.yaml

@@ -9,7 +9,6 @@
     gate:
       queue: tripleo
       jobs:
-        - tripleo-ci-centos-7-3nodes-multinode
         - tripleo-ci-centos-7-nonha-multinode-oooq
 
 - project-template:
@@ -81,6 +80,7 @@
     run: playbooks/tripleo-ci/run.yaml
     post-run: playbooks/tripleo-ci/post.yaml
     timeout: 10800
+    voting: false
     nodeset: legacy-centos-7-3-node
     branches: ^(?!stable/(newton|ocata|pike)).*$
     vars: