[Libosinfo] More device drivers v2

[Zeeshan Ali (Khattak)]

Just like v1, these patches add information about virtio and QXL device drivers, make it possible for apps to automatically install them as part of Windows XP installation and improve drivers-related API. I'll look into getting virtio/QXL driver installation to work for Windows 7 soon but first I'd want to get these changes in so that we can add this feature in Boxes before the feature- and API/ABI-freeze of GNOME 3.7.x[1].

Changes since v1:

* Since disabling drivers signature checks permanently is a security issue, Apps now must explicity disable it.
* Driver signing requirement of scripts is not a simple boolean now but rather an enum.
* Drivers in executable format must provide script (.cmd in case of windows) files that calls the actual setup
  binary with the appropriate arguments for us.
* Scripts can (at least theoretically) support multiple driver formats now.

Issues:

* I get a blue screen of death[2] on Windows XP professional at the end of installation. Christophe tells me that this probably will be fixed with the next spice-guest-tools binary with up2date vioser drivers. That is hopefully available before these patches are merged but for now the work around is to simply reboot the VM (virsh reboot VM_NAME).

[1] https://live.gnome.org/ThreePointSeven#Schedule
[2] http://static.fi/~zeenix/tmp/blue-screen-of-death.png