$ virsh vol-clone /tmp/test.iso new.iso
error: Failed to clone vol from test.iso
error: internal error: Child process (/bin/qemu-img convert -f iso -O iso /tmp/test.iso /tmp/new.iso) unexpected exit status 1: qemu-img: Could not open '/tmp/test.iso': Unknown driver 'iso'

Map iso->raw before sending the format value to qemu-img

https://bugzilla.redhat.com/show_bug.cgi?id=972784
https://bugzilla.redhat.com/show_bug.cgi?id=1419395