Updates available immediately after updating the system

[hinnerk]

In some cases freshly pulled docker images on different machines have different ids. This makes the update system believe that a more recent version of that image is available. Unfortunately, pulling the image again does not fix this bug.

[hinnerk]

Found it:

We're still using docker registry API V1 which was disabled in favor of V2 a few days ago. So now we need to switch to V2.

---

V2 answers under https://registry.hub.docker.com/v2/repositories/experimentalplatform/dokku/tags/development/ with:

{
    "creator": 347439,
    "full_size": 158058043,
    "id": 405642,
    "image_id": null,
    "last_updated": "2015-10-28T10:26:25.923657Z",
    "last_updater": 347439,
    "name": "development",
    "repository": 236958,
    "v2": true
}

While V1 was answering under https://index.docker.io/v1/repositories/experimentalplatform/dokku/tags/development with:

[
    {
        "id": "d7163fb7",
        "pk": 0
    },
    {
        "id": "661e89a8",
        "pk": 0
    },
    {
        "id": "7534ff6c",
        "pk": 0
    },
    {
        "id": "577b1fa9",
        "pk": 0
    },
    {
        "id": "b3f5c30d",
        "pk": 0
    },
    {
        "id": "399c7853",
        "pk": 0
    },
    {
        "id": "7573507c",
        "pk": 0
    },
    {
        "id": "67402719",
        "pk": 0
    },
    {
        "id": "6a47f0b1",
        "pk": 0
    },
    {
        "id": "3d5973fe",
        "pk": 0
    },
    {
        "id": "1e3bad19",
        "pk": 0
    },
    {
        "id": "688a37f6",
        "pk": 0
    },
    {
        "id": "10e887b5",
        "pk": 0
    },
    {
        "id": "82df9b23",
        "pk": 0
    },
    {
        "id": "133b6bc6",
        "pk": 0
    },
    {
        "id": "380693aa",
        "pk": 0
    },
    {
        "id": "15cd271d",
        "pk": 0
    },
    {
        "id": "17542755",
        "pk": 0
    },
    {
        "id": "f861e956",
        "pk": 0
    },
    {
        "id": "cac88573",
        "pk": 0
    },
    {
        "id": "2d03dd68",
        "pk": 0
    },
    {
        "id": "640e351f",
        "pk": 0
    },
    {
        "id": "b4227136",
        "pk": 0
    },
    {
        "id": "fd575666",
        "pk": 0
    },
    {
        "id": "1705bc45",
        "pk": 0
    },
    {
        "id": "4d5d3221",
        "pk": 0
    },
    {
        "id": "09c41809",
        "pk": 0
    },
    {
        "id": "6b458ab0",
        "pk": 0
    },
    {
        "id": "ff79548c",
        "pk": 0
    },
    {
        "id": "c7179b5d",
        "pk": 0
    },
    {
        "id": "81ebaca6",
        "pk": 0
    },
    {
        "id": "a91e97be",
        "pk": 0
    },
    {
        "id": "de192948",
        "pk": 0
    },
    {
        "id": "c13e70d1",
        "pk": 0
    },
    {
        "id": "0a93a7d3",
        "pk": 0
    },
    {
        "id": "2cb77cf6",
        "pk": 0
    },
    {
        "id": "a3b54e9b",
        "pk": 0
    },
    {
        "id": "1523bcaf",
        "pk": 0
    },
    {
        "id": "da6a6c3b",
        "pk": 0
    },
    {
        "id": "735d5ec2",
        "pk": 0
    },
    {
        "id": "32a91bb0",
        "pk": 0
    },
    {
        "id": "376a5d18",
        "pk": 0
    },
    {
        "id": "0421e72a",
        "pk": 0
    },
    {
        "id": "5ac0b283",
        "pk": 0
    },
    {
        "id": "c3fd9360",
        "pk": 0
    },
    {
        "id": "5d2640c2",
        "pk": 0
    },
    {
        "id": "21cd77e3",
        "pk": 0
    },
    {
        "id": "2bcd98b7",
        "pk": 0
    },
    {
        "id": "82554298",
        "pk": 21317066
    },
    {
        "id": "08ab0937",
        "pk": 21317065
    },
    {
        "id": "9f5beeea",
        "pk": 21317064
    },
    {
        "id": "b8b73eaa",
        "pk": 21317063
    }
]