Affinity router pre-pairing & votha rw/ro core DNS.

This requires changes to afrouterd to work correctly, please consider/merge both patches together.

- Added headless services for all RW cores.
- Changed RO cores to use a StatefulSet.
- Added a service for the RO cores.
- Modified afrouter config to use pre-configure core connectivity.

Change-Id: I6a29097e446f46fa2a02e1f9213a840af283a18f
diff --git a/voltha/templates/ro-core.yaml b/voltha/templates/ro-core.yaml
index 7a60699..de2e2c6 100644
--- a/voltha/templates/ro-core.yaml
+++ b/voltha/templates/ro-core.yaml
@@ -30,16 +30,31 @@
 {{- end }}
 
 ---
-apiVersion: apps/v1
-kind: Deployment
+apiVersion: v1
+kind: Service
 metadata:
-  name: ro-core
+  name: voltha-ro-core
+spec:
+  ports:
+    - name: grpc
+      port: 50057
+  clusterIP: None
+  selector:
+    app: ro-core
+
+---
+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: voltha-ro-core
   serviceAccountName: {{ .Values.serviceaccount }}
 spec:
   replicas: {{ .Values.replicas.ro_core }}
   selector:
     matchLabels:
       app: ro-core
+  serviceName: voltha-ro-core
+  podManagementPolicy: Parallel
   template:
     metadata:
       labels:
@@ -55,16 +70,14 @@
     spec:
       affinity:
         podAntiAffinity:
-          preferredDuringSchedulingIgnoredDuringExecution:
-          - weight: 100
-            podAffinityTerm:
+          requiredDuringSchedulingIgnoredDuringExecution:
+            - topologyKey: "kubernetes.io/hostname"
               labelSelector:
                 matchExpressions:
-                - key: app
-                  operator: In
-                  values:
-                  - ro-core
-              topologyKey: "kubernetes.io/hostname"
+                  - key: app
+                    operator: In
+                    values:
+                    - ro-core
       serviceAccountName: {{ .Values.serviceaccount }}
       containers:
         - name: voltha