After discussing with @samalba, we've seen that the VBox modules are pretty small.

Considering there is still a lot of work to do before NFS and/or SMB becomes a viable option, I'm proposing we include them in the image, at least for now.

Sure, it won't be the fastest thing. Sure, it will tie us to VBox (we are anyway via boot2docker-cli), but it will relieve a lot of pain for our users, in the interim of a better solution.

They will be built in rootfs/Dockerfile

-rw-r--r-- 1 root root 376K Feb 27 01:13 vboxguest.ko
-rw-r--r-- 1 root root  70K Feb 27 01:13 vboxsf.ko
-rw-r--r-- 1 root root 6.6K Feb 27 01:13 vboxvideo.ko