Add org.opencontainers.image.* labels to Dockerfiles

- 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
- Git revision (`git rev-parse HEAD`) is now injected at `docker build` time.

docker/Dockerfile.scope

@@ -7,3 +7,10 @@ COPY ./run-app /etc/service/app/run
 COPY ./run-probe /etc/service/probe/run
 EXPOSE 4040
 ENTRYPOINT ["/home/weave/entrypoint.sh"]
+
+ARG revision
+LABEL maintainer="Weaveworks <help@weave.works>" \
+      org.opencontainers.image.title="scope" \
+      org.opencontainers.image.source="https://github.com/weaveworks/scope" \
+      org.opencontainers.image.revision="${revision}" \
+      org.opencontainers.image.vendor="Weaveworks"