[Review] Request from 'aduffeck' @ 'SUSE/machinery/review_140804_use_static_ssh_key'

Please review the following changes:
  * af8b121 Get rid of pennyworth dependency in the machinery VMs
  * ca21ccd Use Os classes to choose network details
  * 53f1bdd Remove stray statement
  * fc0f50f Use native Os objects when checking for platform
  * b8b1c23 Simplify mocking of host Os
  * ee2eefb Remove obsolete code
  * e459e5c Fix conflict due to exception changes
  * 1ece151 Refactor Os detection
  * 4d26756 Move display names of Os to Os class
  * 6d7febc Rename LocalSystem.os to os_object
  * 42eeef3 Allow can_build? to also receive an instance of Os
  * a708cb7 Add method to return Os object for local host
  * 47f5c1d Add SystemDescription method to get Os instance
  * 35a3537 Define basic Os classes