cmd/cork: add download-image command
cmd/cork: add download-image command

dm0-/mantle,quantum/coreos-mantle,dm0-/mantle,mjg59/mantle,mischief/mantle,marineam/mantle,glevand/coreos--mantle,mischief/mantle,glevand/coreos--mantle,quantum/coreos-mantle,marineam/mantle,mjg59/mantle