Only install the drivers that where previously validated by
_fetch_virtio_drivers()

 * Detect the VirtIO driver type by the Device ID it refers to and not
   the catalog file name
 * Check if a driver is suitable for the input media by examining the
   TargetOSVersion field

When installing new drivers, make sure the old ones get uninstalled.

Rewrite the virtio_dir_check function that checks if a given directory
is indeed hosting VirtIO drivers.

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

Collect more detailed information about the installed VirtIO drivers

Make install_virtio_drivers a public method of the class Windows

When installing the virtio drivers monitor the booting process of
the windows VM

Support installing virtio drivers in Windows 8, 8.1, 2012 and 2012R2

Remove mount and unmount methods and add a mount context manager for
mounting the media file systems.

This method can be used to compare the OS version against one specified
by the user.

Add a powershell script in the input media that will properly install
the virtio drivers in the next boot.

Upload the virtio drivers to the media and add the drivers directory to
the DevicePath Registry key

It is used many cases and it is better if we cache it.

Add this helper lambda function that can be used to update the value of
type REG_EXPAND_SZ

Add a dirty way to install the viostor driver in windows in order
to make them bootable. This works on Windows 2008R2

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

Fix a bug where "$s" instead of "%s" was used in a string as a
placeholder.

This fixes #17

Small fixes and code beautification.

Extend the SysprepParam class to support defining a custom check
function which can be used to check if the value given by a user when
updating a sysprep parameter is valid.

Those lambda functions are used to set a value of type REG_SZ,
REG_DWORD and REG_BINARY in a registry node

This attribute hosts the block device associated with this Disk
instance. This can be the original media if the source media is a block
device, a loop device of the original media if the original media is a
regular file or a loop device of a temporary object if the original
media is a directory.

Changes include:

 * Break windows.py into multiple modules.
 * Rewrite sysprep parameters mechanism and add a menu entry for this
   in snf-image-creator expert mode.
 * Detect if the media is already sysprepped before performing further
   customizatog.
 * Don't ask for windows password before customization (reset it if needed)
 * Detect if the virtio drivers are installed in the media.
   If not refuse to perform the customization.

Use the @property decorator instead of the property() method to create a
read-only os attribute in Image class.

pep8 1.5 introduced a new test (E265) to ensure there's at least one
space before block comment.

Now that all sysprep parameters are optional, wizard page is no longer
needed.

Add a current_control_set property in Registry class. This way the
CurrentControllSet registry key is only computed once.

 * 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

There is no need to use PowerShell to write the random token to the
serial port. Doing 'echo token > COM1' will do the trick.

 * Mount silently when mounting ro
 * Add a warning if no inspection method is available
 * In Windows put the "Preparing system for image creation" before
   mounting takes place

Add the _mount_error attribute in OSBase. If mount fails, the error
message is written there.

If the virtio drivers are not installed on the media, raise a FatalError

We used to check for the presence of the winexe executable in the
Windows __init__ function. This is not optimal. The winexe check
should be done during customization. The user should be able to
dump, upload or register an image without having Winexe installed.

Make it more general. Till know it was only used for selecting the input
media but other parts of the program should also make use of it.

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

Add code to check if the source media is a sysprepped windows image. If
so, don't allow it to be further customized.

This resolves #6

Don't ask the user to enter an Administrator password before cleaning up
a Windows image. Reset the password before starting the process and
assign the old value if needed at the end.

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.

This modules hosts the Registry class which contains all the registry
manipulation code previously hosted under the Windows class