rgw: add suport for creating S3 type subuser of admin rest api

rgw: add suport for creating S3 type subuser of admin rest api

Fixes: http://tracker.ceph.com/issues/16682
The original code cannot support create s3 type subuser of admin rest api as when i execute the following command:

  ./s3curl.pl --id=personal --put -- http://radosgw.h3c.com:8000/admin/user?subuser\&uid=yrf2\&subuser=yrf2:yrf1\&key-type=s3 -v

it would return msg as follows :

	 < HTTP/1.1 403 Forbidden
	< Date: Thu, 14 Jul 2016 07:04:40 GMT
	* Server Apache/2.4.7 (Ubuntu) is not blacklisted
	< Server: Apache/2.4.7 (Ubuntu)
	< x-amz-request-id: tx00000000000000006608f-0057873988-8551-slave
	< Accept-Ranges: bytes
	< Content-Length: 114
	< Content-Type: application/json
	<
	* Connection #0 to host slave.com left intact
	{"Code":"InvalidAccessKeyId","RequestId":"tx00000000000000006608f-0057873988-8551-slave","HostId":"8551-slave-us"}

 But i have modified the codes for support it ,and it will return actual msg as follows :

  "subusers": [
        {
            "id": "yrf2:yrf1",
            "permissions": "<none>"
        }
    ],
    "keys": [
        {
            "user": "yrf2",
            "access_key": "B46PXYFEWUX0IMHGKP8C",
            "secret_key": "2JYxywXizqwiiMd74UXrJdSJMPNlBtYwF5z8rNvh"
        },
        {
            "user": "yrf2:yrf1",
            "access_key": "INO55WXJ7JQ1ZZGSAB6B",
            "secret_key": "GgCKEfF9hArV2hglunbO7KtvKZnbhmsDpqjSj5DL"
        }
    ],

Please check it ,thanks .

Signed-off-by: snakeAngel2015 <li.jieA@h3c.com>