Remove unused configuration for prometheus-openstack-exporter

The Prometheus OpenStack exporter was needlessly configured to use the
prometheus Docker volume and change permissions of /data, which does
not exist in the container image.

This must have been copy-pasted from existing Prometheus code.

Change-Id: I96017c17e68ca7a00a2d5ac41f2f43ef87694514

ansible/roles/prometheus/defaults/main.yml

@@ -221,7 +221,6 @@ prometheus_openstack_exporter_default_volumes:
   - "/etc/localtime:/etc/localtime:ro"
   - "{{ '/etc/timezone:/etc/timezone:ro' if ansible_os_family == 'Debian' else '' }}"
   - "kolla_logs:/var/log/kolla/"
-  - "prometheus:/var/lib/prometheus"
 prometheus_elasticsearch_exporter_default_volumes:
   - "{{ node_config_directory }}/prometheus-elasticsearch-exporter/:{{ container_config_directory }}/:ro"
   - "/etc/localtime:/etc/localtime:ro"

ansible/roles/prometheus/templates/prometheus-openstack-exporter.json.j2

@@ -9,11 +9,6 @@
         }
     ],
     "permissions": [
-        {
-            "path": "/data",
-            "owner": "prometheus:kolla",
-            "recurse": true
-        },
         {
             "path": "/var/log/kolla/prometheus",
             "owner": "prometheus:kolla",

releasenotes/notes/remove-prometheus-volume-from-openstack-exporter-f6bb5da3093abef8.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    No longer configures the Prometheus OpenStack exporter to use the
+    ``prometheus`` Docker volume, which was never required.