Got this error while trying to update an old VM. I know that continuously updating a box over a long time is not the recommended usage for MW-Vagrant so I don't expect support for this, just sharing in case someone already ran into it and has a workaround. (I guess just deleting /etc/hhvm/php.ini would work?)
==> default: Error: /Stage[main]/Hhvm/File[/etc/hhvm/php.ini]/ensure: change from directory to file failed: Could not set 'file' on ensure: Is a directory - (/etc/hhvm/php.ini20150123-3988-1vknbbk, /etc/hhvm/php.ini) at 72:/tmp/vagrant-puppet-5/modules-0/hhvm/manifests/init.pp