Add pod disruption budget for neutron

This PS adds a pod disruption budget for neutron server

Change-Id: I512d97c5dba281af21cc767a3744e2f5c05c7019

neutron/templates/pdb-server.yaml

@@ -0,0 +1,9 @@
+apiVersion: policy/v1beta1
+kind: PodDisruptionBudget
+metadata:
+  name: neutron-server
+spec:
+  minAvailable: {{ .Values.pod_disruption_budget.server.min_available }}
+  selector:
+    matchLabels:
+      app: neutron-server

neutron/values.yaml

@@ -43,6 +43,10 @@ upgrades:
     max_unavailable: 1
     max_surge: 3
 
+pod_disruption_budget:
+  server:
+    min_available: 0
+
 labels:
   # ovs is a special case, requiring a special
   # label that can apply to both control hosts