Make local mode the default

As per https://github.com/opscode/chef-rfc/pull/48
@adamedx if you have clients and no cookbooks, then you have no cookbooks :)  The scenario is generally there for "chef-client x.rb".  The goal here is that after the first time you run chef-client x.rb, you will no longer see a warning "could not detect your Chef repository" because the clients directory will exist.