compile boot2docker-cli with a docker container

```
docker build -t golang .
# change GOOS=[linux|windows|darwin] and GOARCH=[386|amd64] to your target plattform
docker run -e GOOS=darwin -e GOARCH=amd64 --name boot2docker-cli golang
docker cp boot2docker-cli:/data/boot2docker .
docker rm boot2docker-cli
```