Fixed MPISolverWrapper's direct call of blackbox internal

Summary:
Changed blackbox call. Removed duplicate 'book_time', 'loss' and 'refresh_time' for cand_results. Removed 'finally' which did not make sense here.
This fixes T28410.

Test Plan: At the moment manually tested. But we should think about a testing strategy for MPI features.

Reviewers: floca

Maniphest Tasks: T28410

Differential Revision: https://phabricator.mitk.org/D483