This MR is based on !2222 (closed) using the implementation made be @utz, but it modifies the createdockerimage.py script such that it expects an install script in the form as introduced in !2230 (merged), i.e., it expects everything to be installed by it. If we like this, we can close !2222 (closed).
This has the advantage that the script does not have to be called from within the module, but can be called from anywhere.
This is WIP because it depends on !2230 (merged), especially on the question if we want to restrict ourselves to this type of install scripts.
Relates #912 (closed), #921 (closed)
part of #883 (closed)