[fedora-virt] user qemu has no access to usb devices

["Tom Horsley" <tom horsley att net>]

I don't know if something is busted in my rawhide setup, or if this is just
a real problem with the new scheme of running as user qemu, but user qemu (on
my system at least), has no access to physical usb devices. I had to change
the qemu.conf file to tell it to run as root before it could attach a usb
device to my windows XP virtual machine.

See https://bugzilla.redhat.com/show_bug.cgi?id=524723#c5