Fix for PEP8's E265.

pep8 1.5 introduced a new test (E265) to ensure there's at least one
space before block comment.
Use @property to create the os attribute in Image

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

This attribute hosts the block device associated with this Disk
instance. This can be the 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.
Add REG_{SZ,DWORD,BINARY} helper funcs in Registry

Those lambda functions are used to set a value of type REG_SZ,
REG_DWORD and REG_BINARY in a registry node
Extend SysprepParam class to include a value check

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
updateing a sysprep parameter is valid.
Add extra virtio sysprep parameter in windows

This parameter points to a directory that hosts virtio drivers for
windows.
windows: Install viostor driver if missing

Add a dirty way to install the viostor driver in windows in order
to make them bootable. After booting we need to reinstall it in a
proper way. This works on Windows 2008R2