vbox: Add support for VirtualBox 4.0

vbox: Add support for VirtualBox 4.0

Add vboxArrayGetWithUintArg to handle new signature variations. Also
refactor vboxArrayGet* implementation to use a common helper function.

Deal with the incompatible changes in the VirtualBox 4.0 API. This
includes major changes in virtual machine and storage medium lookup,
in RDP server property handling, in session/lock handling and other
minor areas.

VirtualBox 4.0 also dropped the old event API and replaced it with a
completely new one. This is not fixed yet and will be addressed in
another patch. Therefore, currently the domain events are supported
for VirtualBox 3.x only.

Based on initial work from Jean-Baptiste Rouault.