Autoupgrade fix

- honor `do_registration` and `reg_server` options ([bnc#897040](https://bugzilla.suse.com/show_bug.cgi?id=897040))
- 3.1.125


- tested by @jsrain (SMT server based autoupgrade passed, the base product was updated and a new extension was added)
It's a fix for https://bugzilla.suse.com/show_bug.cgi?id=897040#c5.