Package make-initrd-pipeline-stateless: Information

- Modified the stateless pipeline method as follows:
  + Actually deactivate LUKS-encrypted host devices;
  + Extract file extended attributes (e.g. capabilities).

- Modified the stateless pipeline method as follows:
  + Avoid attempting to unmount the host filesystem in overlay mode;
  + Deactivate LUKS-encrypted host devices that are unmounted;
  + Treat comma (,) in the same way as the pipe symbol (|) when processing the
  STATELESS_IMAGES variable;
  + When unpacking subsequent image layers, use the /etc/passwd and /etc/group
  files from preceding image layers.

- Initial build.