This stops the error message spam when running unprivileged
libvirtd:
2014-06-30 12:38:47.990+0000: 631: error : virPCIDeviceConfigOpen:300 :
Failed to open config space file
'/sys/bus/pci/devices/0000:00:00.0/config': Permission denied

Reported by Daniel Berrange:
https://www.redhat.com/archives/libvir-list/2014-June/msg01082.html