Generalizable guide to convert .dmg to .iso bootable for Lion to Sierra
There's a script for that:


https://github.com/rtrouton/create_macos_vm_install_dmg


It's a pretty straight forward process, finding the bootable portion of the installer, making temporary files, calling asr to restore to the temporary image, convert to ISO, and then name the files with the version of the OS. With all the changes from 10.7 to 10.12 - there are some special cases in the script, but it's quite general in that it works and you can see what it's doing should it break in the future and Rich and the team that collaborate don't find and fix things before we do.