Add opencontainers labels to dockerfiles

Why? What?

This should ultimately help for image-to-code back references.
org.label-schema.* labels are now deprecated, in favour of org.opencontainers.image.* labels. See also: https://github.com/opencontainers/image-spec/blob/master/annotations.md#back-compatibility-with-label-schema
MAINTAINER is deprecated, in favour of the maintainer label.
Git revision (git rev-parse HEAD) is now injected at docker build time.

Testing:

$ docker inspect quay.io/weaveworks/build-golang
[
    {
        [...]
        "ContainerConfig": {
            [...]
            "Labels": {
                "maintainer": "Weaveworks <help@weave.works>",
                "org.opencontainers.image.revision": "248def1ba24b8c48dc05f8f46d0f4a9c2a671e5e",
                "org.opencontainers.image.source": "https://github.com/weaveworks/build-tools/tree/master/build/golang",
                "org.opencontainers.image.title": "golang",
                "org.opencontainers.image.vendor": "Weaveworks"
            }
[...]

$ docker inspect quay.io/weaveworks/build-haskell
[
    {
        [...]
        "ContainerConfig": {
            [...]
            "Labels": {
                "maintainer": "Weaveworks <help@weave.works>",
                "org.opencontainers.image.revision": "248def1ba24b8c48dc05f8f46d0f4a9c2a671e5e",
                "org.opencontainers.image.source": "https://github.com/weaveworks/build-tools/tree/master/build/haskell",
                "org.opencontainers.image.title": "haskell",
                "org.opencontainers.image.vendor": "Weaveworks"
            }
[...]

$ docker inspect weaveworks/socksproxy
[
    {
        [...]
        "ContainerConfig": {
            [...]
            "Labels": {
                "maintainer": "Weaveworks <help@weave.works>",
                "org.opencontainers.image.revision": "248def1ba24b8c48dc05f8f46d0f4a9c2a671e5e",
                "org.opencontainers.image.source": "https://github.com/weaveworks/build-tools/tree/master/socks",
                "org.opencontainers.image.title": "socks",
                "org.opencontainers.image.vendor": "Weaveworks"
            }
[...]

weaveworks / build-tools

Add opencontainers labels to dockerfiles #132