Vagrant configuration for testing Linuxbrew.

To use:

• brew install vagrant Caskroom/cask/virtualbox
• git clone https://github.com/tdsmith/vagrant-linuxbrew.git
• cd vagrant-linuxbrew
• vagrant up --provider virtualbox (centos6|ubuntu)
• vagrant ssh (centos6|ubuntu) -- brew tests (this actually fails right now but it does run!)