Chef Zero provisioner does not respect require_chef_omnibus config

[schisamo]

This was originally reported as part of #240.

TL;DR

The Chef Zero provisioner instantiates an instance of Chef::Application::Client when running chef-client that does not match the instance's Omnibus Chef install. This means that if a user declares Chef 11.4.4 via their .kitchen.yml like so:

driver_config:
  require_chef_omnibus: 11.4.4

the actual chef-client run will use the latest version of Chef (currently 11.8.0).

Longer explanation of issue

In the past when we installed knife-essentials and chef-zero into the Omnibus Chef's GEM_PATH that version of Chef was used for the chef-client run. Now that we sandbox the knife-essentials and chef-zero install into an isolated GEM_PATH the latest version of Chef is also installed via a knife-essentials dependancy. It's probably easiest to just render a client.rb file and shell-out and run /opt/chef/bin/chef-client directly.