"local_mode by default" proposal

With this proposal, new users who type `chef-client x.rb` or `knife` will start in local mode without having to type `-z`.
The use case where you type 'knife cookbook upload foo' and you've cd'd out of your knife config and it spins up a chef-zero server and uploads the cookbook (and then tears down the chef-zero server when you exit?) seems a bit odd to me.  I might be misunderstanding how that would work, in which case being a bit more explicit about how the use case works would be good here.