ppa-assigner: private_only is hardcoded and confusing

private_only is set to False in unit_config, however it needs to be set to True for a pool of private PPAs to work at all. It's name is confusing. As currently implemented, it being set to false does not produce a full set of PPAs, regardless of whether they're public or private. Instead, setting it false only produces a set of public PPAs.

Because it's currently hardcoded, we need to hack in that setting to True before deploying with private PPAs.

Original report follows:
I noticed on a fresh deploy, a ticket I submitted sat in the pending state for ages. I exposed jenkins and had a look:

11:15:24 INFO lander_service_wrapper: Calling via POST [http://10.0.0.243:8080/api/v1/ppa/]: {'ticket_id': u'1'}
11:15:24 WARNING root: No free PPAs can be found. Retrying in 120s

Okay, that seemed odd, but sure enough this was the case:

curl --dump-header - -H "Content-Type: application/json" http://10.0.0.243:8080/api/v1/ppa/ -X POST --data '{"ticket_id": 1}'

HTTP/1.1 404 NOT FOUND
Server: gunicorn/0.13.4
Date: Fri, 14 Mar 2014 11:13:16 GMT
Connection: close
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8

No free PPAs exist in pool

Now, the weird part is that none of these PPAs are marked as unavailable in the database:

{
    "meta": {
        "limit": 20,
        "next": null,
        "offset": 0,
        "previous": null,
        "total_count": 6
    },
    "objects": [
        {
            "id": 1,
            "name": "ppa:ci-engineering-<redacted>-2/ci-pool-2-001",
            "private": true,
            "resource_uri": "/api/v1/ppa/1/",
            "state": 0,
            "ticket_id": 0,
            "timestamp": "2014-03-14T09:55:41.688596"
        },
        {
            "id": 2,
            "name": "ppa:ci-engineering-<redacted>-2/ci-pool-2-003",
            "private": true,
            "resource_uri": "/api/v1/ppa/2/",
            "state": 0,
            "ticket_id": 0,
            "timestamp": "2014-03-14T09:55:41.690413"
        },
        {
            "id": 3,
            "name": "ppa:ci-engineering-<redacted>-2/ci-pool-2-002",
            "private": true,
            "resource_uri": "/api/v1/ppa/3/",
            "state": 0,
            "ticket_id": 0,
            "timestamp": "2014-03-14T09:55:41.691897"
        },
        {
            "id": 4,
            "name": "ppa:ci-engineering-<redacted>-2/ci-pool-2-005",
            "private": true,
            "resource_uri": "/api/v1/ppa/4/",
            "state": 0,
            "ticket_id": 0,
            "timestamp": "2014-03-14T09:55:41.693143"
        },
        {
            "id": 5,
            "name": "ppa:ci-engineering-<redacted>-2/ci-pool-2-004",
            "private": true,
            "resource_uri": "/api/v1/ppa/5/",
            "state": 0,
            "ticket_id": 0,
            "timestamp": "2014-03-14T09:55:41.694276"
        },
        {
            "id": 6,
            "name": "ppa:ci-engineering-<redacted>-2/ci-pool-2-006",
            "private": true,
            "resource_uri": "/api/v1/ppa/6/",
            "state": 0,
            "ticket_id": 0,
            "timestamp": "2014-03-14T09:55:41.695418"
        }
    ]
}