Feature image format support

Make sure the guestfs VM is killed before we launch the VM that
installs the VirtIO drivers.

snf-image-creator can work with different image formats nowadays.

Only use the device mapper when snapshotting block devices. If the
input media is a regular file, then create a qcow2 image and define
the original media as backing_file.

Use qemu-nbd to export a QEMU image as raw where needed

This used to be a class in the util module, but since this is only used
on the Image, it suits better there.

When snapshotting make sure that the size of the underlying block
device is equal to the input media's virtual size. If the input media
is not raw, the QEMU image driver may grow the underlying image. The
block device should be big enough to allow this kind of operations.

This can be used to act on the original media instead of a device-mapper
snapshot.

This resolves #10

There is no need to associate a loop device with the input media if we
are not snapshotting the input media. The loop device is only needed in
order to use the media with the device-mapper.

If a command needs root privileges use # as prompt. In any other case
use $.

Add a section on how to use snf-image-creator on non-raw format images

If qemu catches a signal, it terminates with 0 and prints a message in
stderr. Try to detect if the process has been terminated by a signal
by examining the stderr.

When the user picks a directory that contains VirtIO drivers, show him
the version of the discovered drivers in the confirmation box.

When working in wizard mode, give the user the ability to revert the
installation of the VirtIO drivers.

Don't treat shrink as a seperated task. Add it in the syspreps menu.

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.

Use _add_cleanup and _cleanup in do_sysprep

This is handy because this way we don't need to unlock the
Administrator account if it is locked. Any user that is in the
Administrators group can do the job.

Better handle the case where shrink querymax does not return any
reclaimable space.

Relative IDs are safer. The Administrator's RID is always 500. The
name may change.

There were cases where a FatalError exception was constructed but never
raised

Fix a bug that affects newer versions of libguestfs where the handler
is erroneously closed in disable_guestfs

In Windows, when enumerating active users, also enumerate users that
are members of the Administrators group.

Import the module itself and not every single constant that is
defined there.

This can be used to fetch a registry node by defining a registry path

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

Feature VirtIO installation.

Automatically install or upgrade the VirtIO drivers on Windows images.
This resolves #7.

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.

If this is enabled, the program will try to install the specified VirtIO
drivers to the image.

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

Add a mechanism in OSBase to add cleanup jobs. Use this mechanism to
cleanup the VirtIO drivers installation.

Add a method for disabling the first-logon animation. This will make
Administrator login faster if the Administrator account was previously
locked.

This is needed if the Administrator account is locked

This can be used to check if the media mounting was successful

Do not install and uninstall the winexe service in every single
execution of vm.rexec(). Only uninstall the service after executing the
last command which is either the sysprep or the shutdown command.