Unify openshift_metrics_server image to standard format

This commit removes openshift_metrics_server_image_version and
openshift_metrics_server_image_prefix to simpler override of
openshift_metrics_server_image. This will allow users to utilize
oreg_url for this component by default.

roles/openshift_metrics/defaults/main.yaml

@@ -4,6 +4,7 @@ openshift_metrics_hawkular_agent_image: "{{ l_os_registry_url | regex_replace(l_
 openshift_metrics_hawkular_metrics_image: "{{ l_os_registry_url | regex_replace(l_openshift_logging_search | regex_escape, 'metrics-hawkular-metrics') }}"
 openshift_metrics_schema_installer_image: "{{ l_os_registry_url | regex_replace(l_openshift_logging_search | regex_escape, 'metrics-schema-installer') }}"
 openshift_metrics_heapster_image: "{{ l_os_registry_url | regex_replace(l_openshift_logging_search | regex_escape, 'metrics-heapster') }}"
+openshift_metrics_server_image: "{{ l_os_registry_url | regex_replace('${component}' | regex_escape, 'metrics-server') }}"
 
 openshift_metrics_start_cluster: True
 openshift_metrics_install_metrics: False

roles/openshift_metrics/templates/metrics-server-deployment.j2

@@ -23,7 +23,7 @@ spec:
       serviceAccountName: metrics-server
       containers:
       - name: metrics-server
-        image: {{openshift_metrics_image_prefix}}metrics-server:{{openshift_metrics_image_version}}
+        image: {{ openshift_metrics_server_image }}
         command:
           - /usr/bin/metrics-server
           - "--source=kubernetes.summary_api:?useServiceAccount=true&kubeletHttps=true&kubeletPort=10250"