Cleanup the dialog_* modules

 * Cleanup Wizard and WizardPage classes in dialog_wizard
 * Fix various pylint warnings
windows: Add traverse function in Registry

This can be used to fetch a registry node by defining a registry path
windows: Change how powershell module is imported

Import the module itself and not every single constant that is
defined there.
windows: Enumarate members of the Admin. group

In Windows, when enumerating active users, also enumerate users that
are members of the Administrators group.
Fix a closed libguestfs handler bug

Fix a bug that affects newer versions of libguestfs where the handler
is erroneously closed in disable_guestfs
Add missing `raise' keywords

There were cases where a FatalError exception was constructed but never
raised
windows: Use RIDs instead of Usernames

Relative IDs are safer. The Administrator's RID is always 500. The
name may change.
windows: Better handle shrink corner cases

Better handle the case where shrink querymax does not return any
reclaimable space.
windows: Disable UAC before booting the windows VM

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.
windows: Use OSBase's cleanup mechanism overall

Use _add_cleanup and _cleanup in do_sysprep
Reimplement the sysprep selection mechanism

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.
Fix minor pylint warning and output messages
Make shrink a sysprep

Don't treat shrink as a seperated task. Add it in the syspreps menu.
Update the documentation with the latest changes
Rephrase various messages
Allow the user to revert the VirtIO installation

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

When the user picks a directory that contains VirtIO drivers, show him
the version of the discovered drivers in the confirmation box.
Detect when qemu gets terminated by a signal

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.
docs: Add a different image formats section

Add a section on how to use snf-image-creator on non-raw format images
docs: Use # as prompt for cmds executed by root

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