[Review] Request from 'vlewin' @ 'SUSE/connect/review_140613__cnt_catch_zypper_command_line_errors_in_suseconnect'

Please review the following changes:
  * 2c930ff mute rubocop
  * 01f8e67 fix system tests
  * cdc1c20 fix zypper tests
  * bfd7bd5 fix system tests
  * 4adebce add ZypperError and SystemCallError
  * 22c198c always calls zypper in a silent mode unless quite=false option is set
  * 535483e use open3 library for system calls