execute parallelamgtest also for multiple ranks

In the current master the AMG fails when executed with multiple ranks. This MR adds the parameters MPI_RANKS and TIMEOUT to the dune_add_test, such that the failure is also detected by the CI.

added bug buildsystem test labels

mentioned in issue #68 (closed)

@nils.dreier I opened !290 (closed) and closed it again after I saw this. I think we should test more of those tests in parallel. At least the last four that require MPI anyway. At least the hierarchy test also currently fails (#68 (closed)).

this should be obsolete if !294 (merged) gets merged

closed