These commands can't be run more than once, so can't be in make_iso.sh

see https://github.com/boot2docker/boot2docker/blob/master/doc/BUILD.md#making-your-own-customised-boot2docker-iso

I use this to build extra testing ISO's for testing.


(and yes @tianon , this is really just reverting your PR, but putting it into one layer)
Can you add a comment above this something like the following? (to make sure I don't re-revert this again later :smile:)
```dockerfile
# Do a few steps that can't be run more than once, which is why they can't be in make_iso.sh
```