Split the base box into one used for dev and one for the tutorial.

Fixes #509, #715.
It'd be nice to add some command line help to this tool. But that can be done in a future branch since this is required pretty urgently.
```
(split-base-box =)[~/.../flocker/admin]$ ./build-vagrant-box --help
Building --help box from /home/richard/projects/HybridLogic/flocker/admin/build-vagrant-box/vagrant/--help.
Running vagrant up

Traceback (most recent call last):
  File "./build-vagrant-box", line 80, in <module>
    main(sys.argv[1:])
  File "./build-vagrant-box", line 76, in main
    build_box(path, 'flocker-' + box, version, branch)
  File "./build-vagrant-box", line 43, in build_box
    run(['vagrant', 'up'], cwd=path.path, env=env)
  File "./build-vagrant-box", line 23, in run
    check_call(command, **kwargs)
  File "/usr/lib64/python2.7/subprocess.py", line 537, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib64/python2.7/subprocess.py", line 524, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/usr/lib64/python2.7/subprocess.py", line 711, in __init__
    errread, errwrite)
  File "/usr/lib64/python2.7/subprocess.py", line 1327, in _execute_child
    raise child_exception
OSError: [Errno 20] Not a directory: '/home/richard/projects/HybridLogic/flocker/admin/build-vagrant-box/vagrant/--help'
```