statistics should be added unit attribute

[Guangyu Suo]

Meter has unit, but Statistics has not :

suo@ustack:~/devstack$ curl -H "X-Auth-Token:$AUTH_TOKEN" http://10.96.24.95:8777/v2/meters/counter-xxx/statistics | ~/devstack/jsontool.py
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 260 100 260 0 0 1122 0 --:--:-- --:--:-- --:--:-- 1125
[
  {
    "count": 3,
    "duration_start": "2013-07-15T15:55:55",
    "min": 200.0,
    "max": 400.0,
    "duration_end": "2013-07-16T07:46:33",
    "period": 0,
    "period_end": "2013-07-16T07:46:33",
    "duration": 57038.0,
    "period_start": "2013-07-15T15:55:55",
    "avg": 300.0,
    "sum": 900.0
  }
]

I think it would be better to add unit to Statistic

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/39545
Committed: http://github.com/openstack/ceilometer/commit/bd4093b8ce9b3ecfd3cd1bee9a51d79da9075ca8
Submitter: Jenkins
Branch: master

commit bd4093b8ce9b3ecfd3cd1bee9a51d79da9075ca8
Author: Gordon Chung <email address hidden>
Date: Wed Jul 31 12:08:26 2013 -0400

    add unit attribute to statistics

    statistics currently aren't associated with a unit it just
    provides sum, average, etc... values without a unit context

    Fixes: Bug#1204458
    Change-Id: Ib92a6a2ab5899a0b269424e94468a73b6559deda