Let the application decide what to do with them. If image-creator
receives an error from kamaki it will terminate. But this may not be
the proper thing to do for an interactive application like
image-creator-dialog

The progress bar of the progress generator had a wrong max attribute.

All image-creator components now output messages using an instance
of one of the output classes.

Also rearrange input options

This is just a template. Not fully workable

Also merge data_cleanup tasks with syspreps and did a major cleanup

All modules should use image_creator.FatalError exception to report
fatal errors.

* Add foreach_file function in OSBase. This is used by all cleanup
  methods
* Add slackware class. This class derives from linux and overwrites the
  log cleanup behaviour. This is needed since slackware stores all
  package management info in /var/log/packages
* Add a shrink method in DiskDevice. This method shrinks the last
  filesystem to the minimum size
* Make the code style comply with pep8