Not collecting ceilometer volume data

[Environment]

Trusty-Mitaka
Charms 16.07

[Description]

Some installations require to gather usage metrics from volumes.

By default those metrics are not enabled:

buntu@niedbalski-sec-bastion:~/openstack-charm-testing$ curl -H X-Auth-Token:$TOKEN http://$CEILOMETER:8777/v2/meters | python -m json.tool|grep -i vol
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 2902 100 2902 0 0 133k 0 --:--:-- --:--:-- --:--:-- 134k

In order to enable this, it is required to set some configuration variables in cinder.conf

control_exchange = cinder
volume_usage_audit_period = hour

AND enable the messaging version 2 notifications:

[oslo_messaging_notifications]
driver = messagingv2

Also, it is required to set a recurring cronjob for gathering the data:

0 * * * * (PYTHONIOENCODING=utf-8 /usr/bin/cinder-volume-usage-audit 1>> /var/log/cinder/cinder_audit_hourly_`date +\%Y\%m\%d`.log 2>&1)

After enabling these configuration directives:

ubuntu@niedbalski-sec-bastion:~/openstack-charm-testing$ curl -H X-Auth-Token:$TOKEN http://$CEILOMETER:8777/v2/meters | python -m json.tool| grep vol
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 8582 100 8582 0 0 38184 0 --:--:-- --:--:-- --:--:-- 38312
        "name": "volume.size",
        "name": "volume",
        "unit": "volume",
        "name": "volume.exists",
        "unit": "volume",
        "name": "volume.size",
        "name": "volume",
        "unit": "volume",
        "name": "volume.exists",
        "unit": "volume",
        "name": "volume.size",
        "name": "volume",
        "unit": "volume",
        "name": "volume.exists",
        "unit": "volume",