extend the Chef provisioner base config object with an 'installer_download_path' property
extend the omnibus command builder with an additional download_path parameter
pass the `download_path` parameter to the `:chef_install` capability so it is available when `Omnibus.build_command(..)` is invoked
don't forget to pass the `installer_download_path` from the config!
Merge pull request #5002 from tknerr/chef-installer-download-path

Add `installer_download_path` config option to chef provisioners