I had the same issue. The command needs to be ran as super user. So make it "sudo virsh define hackintosh.xml"
My problem is now trying to get the iso to boot. For some reason I cannot boot the iso. Everything is set in the bios and in the VM settings. It just boots to nothing. When I try to manually boot from the CD ROM I made, the screen just blinks and comes back to the bios screen. I tried remaking the iso, but nothing changed.