Updating to Vagrantfile version 2 and more.

* Updating to Vagrantfile version 2
* Adding the option to limit the number of CPUs
* Limiting the max CPU usage
* :public_network will ask you which NIC you want to bridge with.
* Move VirtualBox stuff under |virtualbox|
Merge pull request #5 from JasonSwindle/patch-1

Updating to Vagrantfile version 2 and more.