Add options for preserving extended atrributes, hard links, ACLs.

 * Fix a bug where the parent process did not wait on the child
   processes.
 * Make sure that when updating the copy progress bar, at least
   0.1 seconds have passed. This guarantees that we do not experience
   any flickering in the progress bar.

Add a new try_fail_repeat function that wraps cleanup system commands
and retries them if they fail. There are cases where commands like
dmsetup, umount and losetup -d may fail with device is busy. In most
of the cases, sleeping for halve a second and retrying does the job.

Replace the UUID entries in fstab and grub files for filesystems that
have beeen recreated.

The exclude patterns should contain relative to the source paths

Also do a code cleanup

The partition table of the image is created correct. The partitions
are not yet filled.

Nothing is working yet

Check the file system usage and accordingly reduce the size of the
last partition in the image.

Create a sparse file under /mnt in the size of the root hard disk
and copy the mbr into this file. Not yet workable.

This is not yet workable but it will host the code for creating
images out of a running system.

Also merge data_cleanup tasks with syspreps and did a major cleanup

This can be used to create a set of by default disabled data_cleanup
and sysprep tasks.

* 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