[CHEF-3612] Make chef-solo respect :ssl_verify_mode during recipe download

http://tickets.opscode.com/browse/CHEF-3612

chef-solo will fail if recipe_url will be hosted on https with self-signed certificate, or if there will be no SSL certificates
configured on system at all (see CHEF-2840).This fix allows to set :ssl_verify_mode = :verify_none (default)
to skip verification of certificates during cookbook download.