(#1976) Added virtual and is_virtual fact on Windows

Without this patch, the virtual and is_virtual fact is not
stablished on Windows computers. This patch fixes the problem,
giving an initial coverage for some hypervisors.

The solution proposed is based on the WMI object
Win32_ComputerSystem, being able to detect the following systems:
HyperV, VirtualBox, Vmware and KVM.