change --sataportcount to --portcount

After setting my hard drive interface to “sata”, I hit a VBoxManage error during the build process: “Unknown option: --sataportcount”.  Looking at the docs for VBoxManage storagectl[1], it appears that this option’s name is actually --portcount (as opposed to --sataportcount).

[1]: https://www.virtualbox.org/manual/ch08.html#vboxmanage-storagectl