Removes monasca_grafana persistent volume

The monasca_grafana docker volume currently persists across container
builds, causing changes to installed plugins during build to be ignored.
This change deletes the volume entirely and forces plugin changes to be
applied via rebuild.

Change-Id: I36e62235a085e5c1955fdb5ae31f603be8ba69bf

ansible/roles/monasca/defaults/main.yml

@@ -296,7 +296,6 @@ monasca_persister_default_volumes:
 monasca_grafana_default_volumes:
   - "{{ node_config_directory }}/monasca-grafana/:{{ container_config_directory }}/:ro"
   - "/etc/localtime:/etc/localtime:ro"
-  - "monasca_grafana:/var/lib/grafana/"
   - "kolla_logs:/var/log/kolla/"
 
 monasca_extra_volumes: "{{ default_extra_volumes }}"