Fixed AutoYast Export/Import

- bnc#885800
- `Export`ed data were in old format (fixed)
- Added test cases for three different `Import` formats
- `Services` and `Targets` were switched to lazy loading (they were reading data in constructor)
- Adapted / fixed test cases
you use different default values here and in ```read``` for ```@targets``` and ```@default_target``` it is strange ... and code duplication when fixed to same values.