[Review] Request from 'vlewin' @ 'SUSE/connect/review_140630_extend_yast_wrapper_to_include_activated_'

Please review the following changes:
  * 284bb3c Merge pull request #124 from SUSE/review_140630_fix_status_call_regression
  * 42df4ae add product_activated? and system_activated? methods to the YAST wrapper class
  * 0d4c87b introduce activated? and adapt registered? method
  * 1bef3ed rename registered? to announced?
  * 509b9d5 Update package files
  * 2202147 Fix status call regression in case of free products

Seeing that `activated?` actually asks SCC, @wstephenson and I just agreed to rename this `credentials?`.