(FACT-3184) Update fact_list_generator task

Author: joshcooper

tasks/fact_list_generator.rake

@@ -4,8 +4,11 @@ desc 'Create a fact list for the specified os'
 task :fact_list_generator, [:os_name] do |_, args|
   ROOT_DIR = Pathname.new(File.expand_path('..', __dir__)) unless defined?(ROOT_DIR)
 
+  unless args[:os_name]
+    raise ArgumentError, "Expected an os name, such as `bundle exec rake 'fact_list_generator[Ubuntu]'`"
+  end
+
   require 'facter/framework/core/file_loader'
-  load_dir(['facts', '**'])
 
   os_hierarchy = Facter::OsHierarchy.new
   hierarchy = os_hierarchy.construct_hierarchy(args[:os_name])