Update default image value for prometheus

This change updates the default image value in the prometheus
chart from newton to wallaby for the helm_test image.

Change-Id: I0f70734a8455661f7705baeed3cafbaf529c56a8

prometheus/Chart.yaml

@@ -15,7 +15,7 @@ apiVersion: v1
 appVersion: v2.25.0
 description: OpenStack-Helm Prometheus
 name: prometheus
-version: 0.1.11
+version: 0.1.12
 home: https://prometheus.io/
 sources:
   - https://github.com/prometheus/prometheus

prometheus/values.yaml

@@ -20,7 +20,7 @@ images:
   tags:
     apache_proxy: docker.io/library/httpd:2.4
     prometheus: docker.io/prom/prometheus:v2.25.0
-    helm_tests: docker.io/openstackhelm/heat:newton-ubuntu_xenial
+    helm_tests: docker.io/openstackhelm/heat:wallaby-ubuntu_focal
     dep_check: quay.io/airshipit/kubernetes-entrypoint:v1.0.0
     image_repo_sync: docker.io/library/docker:17.07.0
   pull_policy: IfNotPresent

releasenotes/notes/prometheus.yaml

@@ -12,4 +12,5 @@ prometheus:
   - 0.1.9 Retrieve backend port name from values.yaml
   - 0.1.10 Use full image ref for docker official images
   - 0.1.11 Update htk requirements
+  - 0.1.12 Update default image value to Wallaby
 ...