update rspec and vagrant-omnibus, add vagrant-berkshelf and vagrant-cachier plugins. Also update the Berksfile to conform to Berkshelf 3 format.
add minimal acceptance test (see #6) in Rakefile
remove vagrant-cachier for now since there is more work to do before it can actually cache the omnibus packages
add `desc` so it shows up in `rake -T`
Merge pull request #18 from tknerr/update-gems

Update gems