first pass at switching from requiring in Berkshelf to shelling out
check if we're running in Bundler before clearing the env

add documentation to berks function
first pass at chef-client support
fix remaining issues with chef_client provisioner using berkshelf CLI
add post install message to gem installation
fix load from file when file is missing
guard against nil values in vagrant config
update post install message to something a bit more appropriate
Merge pull request #210 from berkshelf/shell-out

Rewrite without using any Berkshelf code