Adds Vagrantfile

The vagrant file setup 2 vm's with the prerequisites already installed.
Resolves issue #262
Updates README with consistent passwords

It is confusing to have both the api and the rabbitmq password be 'secret'. This changes the rabbitmq password to 'correct-horse-battery-staple'. This is also the passwords that are used in the vagrant file.
Deletes guest user
Merge pull request #276 from spuder/vagrant

Vagrant
Merge pull request #274 from adamcrews/sensu_gem_provider

Add sensu_gem package provider
Update sensu_gem provider

* Added the feature install_options to the provider.
* Updated package install to use the sensu_gem provider if using
  the embedded ruby.