Use ISO 9660 format in create_iso under darwin

Currently `create_iso` in darwin produces CD image with hybrid format HFS+ISO 9660
This is less interoperable than ISO 9660 alone. In particular, CD label is not readable by the udev and breaks some automated configuration system.

Author: eszense

plugins/hosts/darwin/cap/fs_iso.rb

@@ -36,7 +36,7 @@ def self.create_iso(env, source_directory, extra_opts={})
           source_directory = Pathname.new(source_directory)
           file_destination = self.ensure_output_iso(extra_opts[:file_destination])
 
-          iso_command = [BUILD_ISO_CMD, "makehybrid", "-hfs", "-iso", "-joliet", "-ov"]
+          iso_command = [BUILD_ISO_CMD, "makehybrid", "-iso", "-joliet", "-ov"]
           iso_command.concat(["-default-volume-name", extra_opts[:volume_id]]) if extra_opts[:volume_id]
           iso_command << "-o"
           iso_command << file_destination.to_s