introduce check_onu_exist_on_discovery flag for openolt adapter

Change-Id: If391627d6823fd416417672e6b8bf4d91bd00c0e
diff --git a/voltha/values.yaml b/voltha/values.yaml
index 2dccaaa..f0118f9 100644
--- a/voltha/values.yaml
+++ b/voltha/values.yaml
@@ -114,7 +114,7 @@
   rw_core:
     registry: '{{ .Values.global.image_registry }}'
     repository: '{{ .Values.global.image_org }}voltha-rw-core'
-    tag: '{{- if hasKey .Values.global "image_tag" }}{{- if .Values.global.image_tag }}{{ .Values.global.image_tag }}{{- else }}3.1.2{{- end }}{{- else }}3.1.2{{- end }}'
+    tag: '{{- if hasKey .Values.global "image_tag" }}{{- if .Values.global.image_tag }}{{ .Values.global.image_tag }}{{- else }}3.1.5{{- end }}{{- else }}3.1.5{{- end }}'
     pullPolicy: '{{ .Values.global.image_pullPolicy }}'
 
 ingress: