[Review] Request from 'aduffeck' @ 'SUSE/machinery/review_140811_add_data_format_attribute'

Please review the following changes:
  * 738f45c Marks descriptions with incompatible data format in "machinery list"
  * 5e720c1 Raise error if the user tries to load a description with old data format
  * 6a591ef Add a format_version attribute to the description meta data