The JSON info files contain details about the created firmware images
per device and are stored next to the created images.

The JSON files are stored as "$(IMAGE_PREFIX).json" and contain some
device/image meta data as well as a list of created firmware images.

An example of openwrt-ramips-rt305x-aztech_hw550-3g.json

    {
      "id": "aztech_hw550-3g",
      "image_prefix": "openwrt-ramips-rt305x-aztech_hw550-3g",
      "images": [
        {
          "name": "openwrt-ramips-rt305x-aztech_hw550-3g-squashfs-sysupgrade.bin",
          "sha256": "db2b34b0ec4a83d9bf612cf66fab0dc3722b191cb9bedf111e5627a4298baf20",
          "type": "sysupgrade"
        }
      ],
      "metadata_version": 1,
      "supported_devices": [
        "aztech,hw550-3g",
        "hw550-3g"
      ],
      "target": "ramips/rt305x",
      "titles": [
        {
          "model": "HW550-3G",
          "vendor": "Aztech"
        },
        {
          "model": "ALL0239-3G",
          "vendor": "Allnet"
        }
      ],
      "version_commit": "r10920+123-0cc87b3b

",
      "version_number": "SNAPSHOT"
    }

Signed-off-by: Paul Spooren <mail@aparcar.org>