ProdNG image generation, getting a secure image.

• Each new image to push is generated from scratch using the latest qualified packages we want to include into it (around 150 base Linux packages).

• Then we have an image diff tool that shows diffs in ASCII files, list of files and permissions between 2 images.

• Package rebuilds revert mtime only changes, and squash binary changes due to dates (like gzip of the same man page gives a new binary each time because gzip encodes the time in the .gz file). Same thing for .pyc files.

• As a result, rebuilding an image with the same input packages is reproducible and gives the same output.