PO-1740: initial commit

Merge http://github.com/acm1/chef-parallel_download
If any of the scripts return non-zero, xargs will also return non-zero, and the `cmd.error!` line will throw an exception, failing the Chef run. I had to add `--fail` to the curl command at https://github.com/acm1/chef-parallel_download/blob/master/providers/default.rb#L51 to get it to fail if it got a 404 error.