Fixed selecting required packages (openssh, SuSEfirewall2) in case of default configuration + minimal sw selection

- Packages are now requested always
- Opens/closes ports as requested by user
- bnc#893126
- includes a little refactoring
- no test case, that require to put everything into lib/network (in TODO)
- tested in production

Good point. I've opened https://github.com/yast/yast-ycp-ui-bindings/issues/21 for that.