create-gentoo-zfs-vm: Use genkernel config instead of passing arguments
genkernel initramfs --virtio --no-clean --no-mountboot --zfs \ --makeopts="-j9 -l8"
which is not too long; but the same command has to be typed whenever the user wants to rebuild the initramfs.
There is an
/etc/genkernel.conf file that has variables for most of these arguments. Set them there, so that rebuilding the initramfs requires just a
genkernel initramfs command.