Adding params for voltha images

Change-Id: I47286050d58dfffdcaee79c07b2b378afb00077e
diff --git a/voltha/templates/10-default-backend.yaml b/voltha/templates/10-default-backend.yaml
index 60f368d..5b2cdb8 100644
--- a/voltha/templates/10-default-backend.yaml
+++ b/voltha/templates/10-default-backend.yaml
@@ -32,7 +32,7 @@
         # Any image is permissable as long as:
         # 1. It serves a 404 page at /
         # 2. It serves 200 on a /healthz endpoint
-        image: gcr.io/google_containers/defaultbackend:1.4
+        image: {{ .Values.httpBackendImage }}
         livenessProbe:
           httpGet:
             path: /healthz