Handle correct extended partitions with id 0xf

Make sure the user cannot select a directory as input media

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.

In Guestfs you get notifications about progress on some functions like
launch() by registring callback functions. When using guestfs from python,
this is fragile. If the callback functions raises an exception, you end up
with segmentation fault. It is better to completely remove the progress
monitoring from launch().

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

Credits go to Giannis Spiliopoulos <gspilio@admin.grnet.gr>

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.

Also, add a warning about LVM, the need for openssh-server, memmory
parameter for KVM and md5sum for the dowloaded iso.

The example has been copied from okeanos-guides. However, some
of the example's steps have been ommited (e.g. the installation of
snf-image-creator). Also, the focus has been shifted from ~okeanos to a
run-of-the-mill synnefo deployment.

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

The older method of installing snf-image-creator from source is restored
and presented alongside the official package installation method.

Drop python installation method in favor of a simpler method using
packages from the apt.dev.grnet.gr repo.

As stated in commit b5053149, these
packages are not needed for the installation of snf-image-creator.

Remove python-gevent and python-dev from the dependencies list for
snf-image-creator. These two packages were needed for kamaki < 0.1
version, but now are obsolete.

This is the initial commit of the okeanos-helpdesk branch.
The main purpose of this branch is to:
* Move non-technical parts (e.g examples) to the okeanos-guides docs,
  where they can be presented in a more user-oriented way
* Correct minor omissions that okeanos-helpdesk has encountered during
  the testing of the image-creator tool

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