Migrating the vagrant image to Centos/7

Changing the organization name `chef` to `bento` fixes the `Vagrantfile`, however I implemented an image using _Centos/7_. I can work on a pull request (the code is working and already tested), but I'm not sure if it will be useful here.

Let me know if it is ok to work on a pull request for this. [Repo](https://github.com/3manuek/Anemometer/tree/master/vagrant)