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[newton][bugfix] Correct faulty exception handler

Timo Koch requested to merge fix/newton-exception-handler into master

What this MR does / why does DuMux need it:

Avoids a deadlock on the Dumux side in case of parallel runs. If one process throws, we make sure to catch the error and only set converged to false. Then, we check if all processes converged and throw on all processes.

Unfortunately, there can still be deadlocks if there is global communication (in Dune) after a process throws (in Dune) within some Dune function (e.g. in the solver). In that case, we cannot easily handle this in Dumux, because the communicating processes are stuck in the Dune function, and only the throwing process makes it back to Dumux. Therefore, we cannot recover (we could terminate after a timeout). See for a discussion of the general problem.

  • Add parallel unit test for newton where the assembler or linear solvers throw on one process (test failed before this bugfix)

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Fixes #1171 (closed)

Edited by Timo Koch

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