Change shelled out calls to Docker remote API

[andystanton]

The approach I've taken to #22 involves more shelled out calls to the Docker CLI. This is getting ugly and there may be a better way: talking to the Docker remote API directly and parsing the json it returns instead of hacking around with the arbitrary text returned by the CLI.

Boot2docker example query piped into jq:

curl \
    --insecure \
    --cert ~/.boot2docker/certs/boot2docker-vm/cert.pem \
    --key ~/.boot2docker/certs/boot2docker-vm/key.pem \
    https://$(boot2docker ip):2376/images/json \
| jq .

Gives a (much longer) version of this response:

[
  {
    "Created": 1422379591,
    "Id": "c90d655b99b2ec5b7e94d38c87f92dce015c17a313caeaae0e980d9b9bed8444",
    "Labels": null,
    "ParentId": "30d39e59ffe287f29a41a3f8bd70734afc8728329e3289945cbdc5bbf07cd980",
    "RepoDigests": [],
    "RepoTags": [
      "debian:latest"
    ],
    "Size": 0,
    "VirtualSize": 85014569
  }
]

In this thread, it's noted that the version of curl that comes with osx doesn't work with the above command (I've confirmed on Yosemite which is curl 7.30.0).

Running the latest curl downloadable through brew (7.42.0 currently) allows the command to work which is something to bear in mind when developing this change as I'm not sure what http libraries are available in go.

[andystanton]

Also useful: link to Docker remote API reference - https://docs.docker.com/reference/api/docker_remote_api/

[andystanton]

go lang docs for network operations: https://golang.org/pkg/net/

[andystanton]

I'm making good progress on this on branch feature/use-docker-remote-api but need to improve my understanding of the language as the Go I'm writing is poor.

[andystanton]

Closing this in favour of #46, in which custom code calling the Docker CLI or remote API will be replaced by a library that does the same job.