Support types for custom meters in collectd_ceilometer_plugin

[Emma Foley]

collectd supports custom types (https://collectd.org/documentation/manpages/types.db.5.shtml#custom_types). Adding custom types are not supported in collectd-ceilometer-plugin as of yet. Extending 'types' by means of collectd-ceilometer-plugin configuration would be nice to have should the need arise.

Needs investigation:
- custom types.db files can be used and should be accessible from the get_dataset() method currently used.
- Custom metric:type mappings could be configured in devstack/configuration
  - this could mean adding the new types to a custom types.db file in collectd configuration

[jaroslavx.safka (jaroslavx-safka)]

Hi,
if you need any special types, then you can create class for them.
See /collectd_ceilometer/common/meters/ and libvirt.py.
And storage.py line 29 where you can override the types witch own class.