[doc] "auth_credential" parameter is invalid

[Yotaro Konishi]

In here: http://cue.readthedocs.org/en/latest/rest/v1/clusters.html, "auth_credential" parameter is listed in the REST API doc, but it is invalid.
"authentication" parameter should be used instead.

Here is the example of the error:
===
curl -g -i -X POST http://192.168.112.203:8795/v1/clusters -H "Content-Type: application/json" -H "X-Auth-Token: $token" -d '{"name": "test", "network_id": ["d9b0681b-b366-495a-9010-07b56ef40a0f"], "volume_size": 0, "auth_credential": {"token": {"username": "guest", "password": "guest"}, "type": "plain"}, "flavor": "3", "size": 1}'
HTTP/1.0 400 Bad Request
Date: Fri, 18 Mar 2016 10:55:36 GMT
Server: WSGIServer/0.1 Python/2.7.5
Content-Type: application/json
Content-Length: 144

{"error_message": "{\"debuginfo\": null, \"faultcode\": \"Client\", \"faultstring\": \"Unknown attribute for argument data: auth_credential\"}"}
===

"authentication" parameter works fine.
===
curl -g -i -X POST http://192.168.112.203:8795/v1/clusters -H "Content-Type: application/json" -H "X-Auth-Token: $token" -d '{"name": "test", "network_id": ["d9b0681b-b366-495a-9010-07b56ef40a0f"], "volume_size": 0, "authentication": {"token": {"username": "guest", "password": "guest"}, "type": "PLAIN"}, "flavor": "2", "size": 1}'
HTTP/1.0 202 Accepted
Date: Fri, 18 Mar 2016 10:45:17 GMT
Server: WSGIServer/0.1 Python/2.7.5
Content-Length: 244
Content-Type: application/json; charset=UTF-8

{"status": "BUILDING", "name": "test", "network_id": ["d9b0681b-b366-495a-9010-07b56ef40a0f"], "created_at": "2016-03-18T10:45:17+00:00", "volume_size": 0, "flavor": "2", "endpoints": [], "id": "bc1ab0c3-8cf1-41ee-95fc-29162329e39d", "size": 1}
===

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/294530

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/294530
Committed: https://git.openstack.org/cgit/openstack/cue/commit/?id=6ec5ebb0eca776add439ed6ca00304b3df0280c5
Submitter: Jenkins
Branch: master

commit 6ec5ebb0eca776add439ed6ca00304b3df0280c5
Author: Yotaro Konishi <email address hidden>
Date: Fri Mar 18 20:26:26 2016 +0900

    Documentation fix: use "authentication" instead of "auth_credential"

    "auth_credential" parameter is invalid. "authentication" parameter should be used.

    Change-Id: Ibf706eaa3d327ef505cc036497bcb1957f7eb793
    Closes-Bug: #1559034