Packer config for the boxes which can be found at https://app.vagrantup.com/russmckendrick/boxes/centos75.
To build both Virtualbox and VMWare boxes run;
packer build CentOS_7.json
For just VMWare;
packer build -only vmware-iso CentOS_7.json
And for Virtualbox;
packer build -only virtualbox-iso CentOS_7.json