Mounted /var/www/ loses www-data permissions on next `vagrant up`

Vagrant allows us to specify a user to mount shared folders with. We would normally mount `/var/www/` as the `www-data` user, but in the CentOS box that we're using, this user isn't available until the machine has been provisioned.

We trick things a bit during provisioning by unmounting the `vagrant` owned `/var/www/` and remounting it under the `www-data` user.

When `vagrant halt` is used with `vagrant up`, the drive is remounted as defined in Vagrantfile and our provisioning is not processed again (which is good).

Need to determine how best to handle the remount as the `www-data` user.