Comment 1 for bug 656173

A temporary workaround in my case is to:
1/ add the denied file in the Template /etc/apparmor.d/libvirt/TEMPLATE :
"/U/libvirt-image/base/lenny_compressed.qcow2" r,
2/ Remove the generated file /etc/apparmor.d/libvirt/libvirt-c05e04f2-fe2e-b8de-c129-bd074c908476*
3/ Reload apparmor and start the VM