virt-sandbox-image: separate templates from the different sources
virt-sandbox-image: separate templates from the different sources

Put templates files in a folder for the corresponding source to avoid
potential name conflicts.

agx/libvirt-sandbox-debian,agx/libvirt-sandbox-debian,agx/libvirt-sandbox-debian,agx/libvirt-sandbox-debian,libvirt/libvirt-sandbox,libvirt/libvirt-sandbox,libvirt/libvirt-sandbox,agx/libvirt-sandbox-debian