Equivalents for genisoimage and qemu-img on Ubuntu
You can use mkisofs instead of genisoimage - they are almost identical (mkisofs is actually newer and better maintained, while genisoimage is debian's old fork of it).
It comes with cdrtools, which you can install from brew:
brew install cdrtools
$ hdiutil makehybrid -o init.iso -hfs -joliet -iso -default-volume-name cidata config/
Where config/ contains meta-data and user-data.
$ brew install gemu