automatically add 'uuid' parameter when passing through NVIDIA vGPU

automatically add 'uuid' parameter when passing through NVIDIA vGPU

When passing through an NVIDIA vGPU via mediated devices, their
software needs the qemu process to have the 'uuid' parameter set to the
one of the vGPU. Since it's currently not possible to pass through multiple
vGPUs to one VM (seems to be an NVIDIA driver limitation at the moment),
we don't have to take care about that.

Sadly, the place we do this, it does not show up in 'qm showcmd' as we
don't (want to) query the pci devices in that case, and then we don't
have a way of knowing if it's an NVIDIA card or not. But since this
is informational with QEMU anyway, i'd say we can ignore that.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>