[WIP] OS X install support

- [x] Install `boot2docker` when running script on OS X
- [ ] Perform `boot2docker` initialisation in `bootstrap.sh` to get `docker` up and running (https://docs.docker.com/installation/mac/)
- [ ] Check setup is persisted after reboot
- [ ] Maybe also install `wget` at the start of `bootstrap.sh` for OS X, as it doesn't ship with it
Yeah, that could be done. Here's the output:

```
$ pacapt -Ss docker
boot2docker  docker
homebrew/completions/docker-completion	     Caskroom/cask/boot2docker
```

Think that bottom row is only there cos I've already installed boot2docker. Why would you prefer to do it this way, out of interest? Seems that `uname` or `$OSTYPE` (http://stackoverflow.com/a/394235/1794732) are very reliable.