Refactoring: Parsing files moved to separate functions
Prefer os-release file to content file

- content file is usually broken and should be only used as a fallback
- there is no content file on a running system and thus returns different
  results comparing to the installation
- this unifies the running system with installation
new changes file entry and new version
Merge pull request #218 from kobliha/product_info

Preferring os-release file to content file while reading the product information (bnc#871261)