Change the sysprep enabling and disabling mechanism to always work
correct. The previous implementation was buggy and would erroneously
"remember" the executed syspreps on a reset.

 * Cleanup Wizard and WizardPage classes in dialog_wizard
 * Fix various pylint warnings

Add a page in the dialog wizard that displays the current state of
the VirtIO drivers of the image and allow the user to update the
installed VirtIO drivers. This page will only be shown if the media
hosts a Windows image.

The sysprep parameters with the hidden attribute enabled are not
displayed to the user.

Merge the Parameter menu entry with Sysprep and add a new entry for
installing VirtIO drivers. This will only be visible in Windows.

This parameter points to a directory that hosts virtio drivers for
windows.

 * Use select_file() to update a "file" sysprep param
 * Switch the order of <Details> and <Update> buttons
 * Use the last visited menu entry as default item

Rewrite the mechanism to have better control on the system preparation
parameters. Also change the way the parameters are updated in the UI.

If the needed sysprep parameters had all default values,
snf-image-creator would crash when trying to run the image
customization. This bug could not be triggered from the current os_type
classes.

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.

When adding a new image property, check if the property already exists
or if it contains invalid characters.

Add functionality for deleting image properties in the "Modify"
menu entry in expert mode and completely remove the "Delete" entry.

When we wrap text to create a paragraph and print it in a dialog box,
make sure the lines will not get wrapped further by the dialog box.

This allows us to add a Description field in register. This can be
used to update the DESCRIPTION image property

This can be used to perform various tests to determine if the media
is supported.

Add a new "Unsupported" os_type class. Images that get created from
unsupported media have the EXCLUDE_ALL_TASKS property enabled.

The program would crash if no image properties were available and
the user chose "Edit properties" or "Delete Properties" in the
customization menu

Group the system preparation tasks to simple and advanced.

Remove constants BOOT_TIMEOUT, SHUTDOWN_TIMEOUT and CONNECTION_RETRIES
and add then as sysprep_parameters

This is needed since the input we get from the input dialogs is
always strings.

Fix some bugs and some other coding issues found using pylint

The user may define parameters needed by the os_type classes to perform
the system preparation tasks.

A new needed_sysprep_params method is added to os_type.OSBase that
returns a list with parameters that should be defined by the user.

python-dialog package in OpenSUSE decorated the returned enabled
choices from a dialog checklist with `"'. Remove those characters

The system preparation tasks could be printed multiple times in the
help dialog.

In the documentation and the printed messages, remove all references
to ~okeanos, pithos or cyclades.

When registring an image, use the information returned by the
kamaki register method to construct the metadata file.

When dumping the image to the local filesystem, store the image
properties and the disk-format info in the metadata file.

 * Change the authentication everywhere to use clouds
   (authentication URL and token pairs)
 * Add menu entries to manage clouds
 * Add an extra -a option in snf-image-creator to allow the user to
   specify authentication URLs

 * 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

If the image gets registered as public allow anyone to read the
metadata and the md5sum file.

Before uploading to pithos, check if any remote file gets
overwritten.

Syspreps that have already been executed shouldn't get returned by
list_syspreps

Check if the filesystem is mounted read-write before you execute
the do_sysprep function