[sahara] make grenade job temporary non-voting

grenade is not stable enough right now, blocking
gate right now. stats of failures at [0]. Looks like
the general blockers are neutron tempest tests.

change should be reverted as soon as it grenade will
be stable enough.

[0]
http://status.openstack.org//openstack-health/#/job/gate-grenade-dsvm-sahara?groupKey=project&resolutionKey=hour&end=2016-05-12T20:40:37.705Z

Change-Id: I88bc28d1d87b537b611d0d44d6a9c127460d571b

zuul/layout.yaml

@@ -1975,6 +1975,9 @@ jobs:
     branch: ^master$
     voting: false
 
+  - name: gate-grenade-dsvm-sahara
+    voting: false
+
   - name: ^gate-sahara-extra-artifacts$
     branch: ^(?!stable/kilo).*$
     voting: false
@@ -10886,7 +10889,6 @@ projects:
       - gate-sahara-dsvm-scenario-neutron-direct-nv
       - gate-sahara-dsvm-scenario-nova-direct-nv
     gate:
-      - gate-grenade-dsvm-sahara
       - gate-sahara-dsvm-scenario-neutron-heat
       - gate-sahara-dsvm-scenario-nova-heat
       - gate-tempest-dsvm-sahara