Set ClusterIP to None for executor logs

The executor logs service needs to be a headless service so that
the scheduler can connect to the specific executor pod running a
job.  Set "ClusterIP: None" for this.

Change-Id: Ib95a344812439f81f1376b33182147c9988e49c9

charts/zuul/templates/executor/service.yaml

@@ -9,6 +9,7 @@ metadata:
 {{- include "zuul.executor.labels" . | indent 4 }}
 spec:
   type: ClusterIP
+  clusterIP: None
   ports:
   - name: logs
     port: 7900