RFC: Reimplemented functionality for handling Kernel modules loaded on boot

Description
- This is a _RFC_ - not yet to be merged, WIP
- /etc/sysconfig/kernel:MODULES_LOADED_ON_BOOT has been moved
  to /etc/modules-load.d/*.conf files
- See also bnc#838185

TODO
- Some function comments are missing
- Do not rewrite files that haven't been modified