Make neutron-tempest-dvr job non-voting

The job is lately very unstable and fails randomly which blocks
other tempest patches. Let's make it temporarily non-voting.

Change-Id: I5f53953c1fa9e88e8406ec6a080314d813137774
diff --git a/.zuul.yaml b/.zuul.yaml
index 5e3f33a..37fad60 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -720,6 +720,7 @@
             voting: false
             irrelevant-files: *tempest-irrelevant-files
         - neutron-tempest-dvr:
+            voting: false
             irrelevant-files: *tempest-irrelevant-files
         - interop-tempest-consistency:
             irrelevant-files: *tempest-irrelevant-files