v2v: Windows: Fix quoting and type of viostor ImagePath parameter.

The way to fix these bugs -- for future reference -- is as follows:

(1) Install the corresponnding Windows version with virtio enabled.
See:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Deployment_and_Administration_Guide/chap-KVM_Para_virtualized_virtio_Drivers.html

(the ".vfd" method)

(2) Download the SYSTEM and SOFTWARE registries from the
virtio-enabled guest.

(3) Examine each registry using 'hivexsh', especially the keys which
we modify during virt-v2v (see v2v/convert_windows.ml).  Remember to
use both the 'ls' and 'lsval' commands in hivexsh.

(4) Download the SYSTEM and SOFTWARE registries from the guest that
fails to boot.

(5) Examine the same registry keys from each registry using 'hivexsh'.

(6) Work out what the differences are, paying particular attention to
quoting and the type of each key (eg. str(1), str(2), etc).

Thanks: Matthew Booth.
v2v: Windows: Add &REV_00 variant, which is used by W2K8R2.