File _multibuild of Package opensuse-leap-dnf-image

<multibuild>
  <flavor>docker-dnf</flavor>
  <flavor>lxc-dnf</flavor>
  <flavor>networkd-dnf</flavor>
  <flavor>docker-microdnf</flavor>
  <flavor>lxc-microdnf</flavor>
  <flavor>networkd-microdnf</flavor>
</multibuild>