Make greande jobs n-v for EM and oldest stable

As discussed in ML thread[1], we are going to
make grenade jobs as non voting for all EM stable and
oldest stable. grenade jobs are failing not and it might take
time to fix those if we are able to fix. Once it jobs are
working depends on project team, they can bring them back to
voting or keep non-voting.

If those jobs are failing consistently and no one is fixing them
then removing those n-v jobs in future also fine.

[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-June/015499.html

StableOnly

Change-Id: Idac1769dcc3d454251ea1d2b7e65960f8f7e2dfa

.zuul.yaml

@@ -19,7 +19,8 @@
         - sahara-tests-tempest-v2
         - openstack-tox-cover:
             voting: false
-        - sahara-grenade
+        - sahara-grenade:
+            voting: false
         - sahara-tests-scenario-py3
     gate:
       queue: sahara
@@ -28,7 +29,6 @@
         - sahara-tests-scenario-v2
         - sahara-tests-tempest
         - sahara-tests-tempest-v2
-        - sahara-grenade
         - sahara-tests-scenario-py3
 
     experimental: