dfu: Allow specifying the output file type for 'dfu-tool read'
dfu: Allow specifying the output file type for 'dfu-tool read'

Guess the file type if it is not explicitly specified.

fwupd/fwupd,superm1/fwupd,hughsie/fwupd,vathpela/fwupd,fwupd/fwupd,vathpela/fwupd,vathpela/fwupd,fwupd/fwupd,fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,superm1/fwupd,hughsie/fwupd,superm1/fwupd,hughsie/fwupd