Fix #38 clarify successful vagrant provision

Now if the provisioning script completes, it prints a success message.

New users are taught through the docs to look for this message.

![image](https://f.cloud.github.com/assets/438648/2399035/4c12b188-a9fb-11e3-85d1-357b2091c7dc.png)

The fact that it wasn't clear what a correctly provisioned machine
looked like prevented me from knowing that my machine was broken
initially. I got the most excellemnt error message `No error message`,
which made me think everything had succeded initially.

Fixes #38