Remove unecessary Vagrant plugins, up the virtualbox version
Remove the last plugin from vagrant (vagrant-berkshelf) since it's not needed
Add back the vagrant plugins array, but leave it empty
Remove job trigger when change is pushed to GitHub
Merge pull request #35 from rightscale-cookbooks/white_14_02_acu152271_upgrade_vagrant_on_CI

Upgrade to a newer version of Vagrant which allows for multiple VM instances to be run