Integrate option to ease rebuilding a base image

[paulmenzel]

Currently running sudo make a second time, Docker uses the existing images from its cache.

I think that this is not desired, but I have not investigated the effects on for example the size of the image if updating the packages in the Dockerfile is enough.

Currently I am thinking about passing the switch --no-cache=true to docker build.

Another workaround is to do sudo git clean -dfx to remove all files, including the roots, not in the repository.

[jmtd]

This is by design, really: it follows the docker default of using its cache. I'd consider adding support for passing --no-cache=true to the docker invocation as an option.