Fix the root device check to support /dev/xvda[1-9] devices

This fixes #52

The base class is named Output. Having a method with the same makes
the code confusing.

When bundling a host, make sure that the UUIDs and the Labels of the
original file systems are preserved.

Fix a bug in host-bundling operation were in some cases the computed
new image size was wrong.

According to the decision of the GRNET Board of Directors,
switch license to GPLv3.

This commit will be propagated to the release
and master branches based on git flow, and the next
release will be licensed as GPLv3.

Fix some bugs and some other coding issues found using pylint

 * Prefix all private methods with _
 * Write missing docstrings
 * Move all public methods above the private ones
 * Add module docstrings where missing
 * Define source code encodings on all modules

In bundling host make sure that the default mount options are enabled
in the newly created file system.

The exclude patterns were wrong and they excluded more files than
they should.

In the bundled image /tmp and /var/tmp file mode bits ended up being
wrong.

Support images that can only be deployed by the user that registers
the image to cyclades

When shrinking partitions, make sure that the shrinked partitions
always starts from the sector the initial partition started. Changing
this may destroy the boot loader.

It behaves different in different pyparted versions and only causes
problems. Let python do the garbage-collection...

The method has different behaviour in python 2.6 and python 2.7.
In python 2.6, os.path.relpath('/proc', '/) will output '../proc'
where in python 2.7 it will output 'proc'.

Use length instead of getLength() to get the size in sectors of a
device.

We used to exclude mount point from rsync with options like this:

 --exclude mount/point/*

This will copy the directory and leave out all files under it. In
some cases, this causes problems because rsync will fail if it
cannot stat the directory and some mount point will only return
stat info to their owner and not root. Even if this wasn't the
case, we cannot determine the real directory attributes. The stat
syscall will return the attributes associated with the mount
options. It's better to completely exclude those mpoints in rsync
and create them explicitly after the command runs. We make them
inherit the mode and the ownership of their parent directory.

The cow file when creating images or the temporary image file when
bundling the host system may be large. Allow the user to overwrite
the directory under which those files get created.

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.