Support better entropy performance on vagrant VMs

Currently the vagrant-puppet deployment use Virtualbox as VM provider. The visualized hardware in Virtualbox does not have good performance on entropy generation since such randomness often collected from hardware sources.
The poor entropy performance directly impact the use in cryptography or use that required random data, which in our case is kerberos. In order to test our code snipes for real world usage instead of suffering on virtual machines, we can improve the entropy performance on VMs using rng-tools when provisioning those test VMs.