[Review] Request from 'schubi2' @ 'yast/yast-autoinstallation/review_140704_tmpfs_autoyast'

Please review the following changes:
  * bde2553 packaging
  * 3207a30 enable tmpfs in autoyast

@kobliha but it is not exactly same as nil? will return true if key exist and is explicitelly set to nil and `has_key?` test if it is at all in map. Ruby maps can have keys with nil value.