You can now do:
virt-builder centos-7.2 --arch aarch64
to get a CentOS 7.2 aarch64 image. The --arch parameter is not required if your host is aarch64, since it defaults to finding the same guest arch as host arch.
Some other things you might try (these work as non-root too):
virt-builder centos-7.2 \ --arch aarch64 \ --size 20G \ --hostname myguest --timezone Europe/London \ --root-password password:123456 \ --update --selinux-relabel virt-install --import --name myguest --ram 2048 \ --disk path=centos-7.2.img,format=raw --os-variant centos7.0
Note there is an updated virt-builder package available which is similar to what RHEL and CentOS will have in 7.3:
https://people.redhat.com/~rjones/libguestfs-RHEL-7.3-preview/
Rich.