Ability to build mini-os images from source

[gorozco1]

The power user needs to be able to build his own mini-os image from source we should provide a doc how to do that and scripts to do so.

Related to #769, #912 #961

[jcvenegas]

I can take a look at this. To docuement how to use os builder. Also we need a way to build:

• hyperstart

@gorozco1 @egernst do you think we need to build systemd as well or only provide to build hyperstart and insert it to an image is enough ?

[gorozco1]

@jcvenegas is up to you, I would like to use moby if that is possible or osbuilder