[PDI-7507] - Get System Info - Hostname - Returns 127.0.0.1


Consist of two parts 
* FIX: Added getHostnameReal() method and its invocations
* Refactoring: all SystemData types (96) delivered to enum SystemDataTypes. Changes really simplify work with types (adding moving)
* Added unit tests for both commits

To merge: FIX first - then Refactor