boot2docker: add cluster bootstrap and doc

- modify `build/` to allow boot2docker on all platform
- add cluster-pod bootstrap manifest to the base `kubernetes` image
- add getting started guide for `boot2docker`
- update cluster-pod manifest to:
  - use `kubernetes` base image
  - explicit `command` with verbose logging
  - point the master to `boot2docker` ip

You should be able to try this at home with:
```
boot2docker up
$(boot2docker shellinit)
docker run -p 10250:10250 -v /var/run/docker.sock:/var/run/docker.sock proppy/kubernetes /kubernetes/kubelet -v=5 -address=0.0.0.0 -hostname_override=10.0.2.15 -etcd_servers=http://10.0.2.15:4001 -config /pods/cluster-pod.yaml
kubecfg -h $(boot2docker ip):8080 list pods
kubecfg -p 8080:80 run nginx 1 kube-nginx
```