Vagrant passwordless sudo to all users

Correct sudoers line for Vagrant, as per [Vagrant Basebox Guidelines](http://docs.vagrantup.com/v2/boxes/base.html).
The difference between the new and the old lines is that vagrant user can now sudo without passwords to all users (not just root). This is especially relevant when provisioning user-specific settings. (Here's a [StackOverflow thread](http://stackoverflow.com/q/21814361) about this)

Most templates had this right already. This just makes sure all of them are correct.