Set up pi image source control and generation using Duckietown's infrastructure

[david-boles]

From Andrea Daniele:

Doing version control on binary files is usually prohibitive, that is why we have a way to reconstruct the Pi image on the cloud every time we want, so that we can VCS the code that generates it.
I believe it makes sense to actually merge the two images so that flashing for Duckiebot or Duckiedrone makes no difference, the code that will run on it will be the only thing that differs
We have a reliable way of creating templated disk images for Raspberry Pi directly on the cloud.
Which means that we create an image (by performing a series of actions on a clean Raspbian image) and then we leave some placeholders around, like in /etc/hostname, so that those can be populated at flash time.
This allows us to keep only one disk image for everybody and then let the user bake in personal information during flash, for example, wifi passwords, etc.