project id is missing for alarm create

with latest devstack, ceilometer, python-ceilometerclient, (2014-11-18), and set env with devstack/accrc/admin/admin

$ ceilometer --debug alarm-threshold-create --name test-project-id --meter instance --threshold 1
DEBUG (client) REQ: curl -i -X 'POST' 'http://127.0.0.1:8777/v2/alarms' -H 'User-Agent: ceilometerclient.openstack.common.apiclient' -H 'Content-Type: application/json' -H 'X-Auth-Token: 51e87a74f9aa4d84b562468a4cc6249e'
DEBUG (client) REQ BODY: {"threshold_rule": {"threshold": 1.0, "meter_name": "instance"}, "project_id": "", "type": "threshold", "name": "test-project-id", "repeat_actions": false}

+---------------------------+--------------------------------------------------------+
| Property | Value |
+---------------------------+--------------------------------------------------------+
| alarm_actions | [] |
| alarm_id | f8910e62-3490-4fc3-8e0d-4a211b06d83f |
| comparison_operator | eq |
| description | Alarm when instance is eq a avg of 1.0 over 60 seconds |
| enabled | True |
| evaluation_periods | 1 |
| exclude_outliers | False |
| insufficient_data_actions | [] |
| meter_name | instance |
| name | test-project-id |
| ok_actions | [] |
| period | 60 |
| project_id | |
| query | |
| repeat_actions | False |
| state | insufficient data |
| statistic | avg |
| threshold | 1.0 |
| type | threshold |
| user_id | dddb336a7f9740b9910ba5eb8f8edeeb |
+---------------------------+--------------------------------------------------------+

Note that project_id is '', actually it should be the admin's project_id

This is because the AuthPlugin we introduced recently, which sets project_id in class attribute opt_names, which will be added to cli_argument with default value '' in openstack/common/apiclient/auth.py