Feature/ff pm coupling fvca cleanup (to be moved into dumux-pub/jaust2020a)

This branch shall be eventually be moved into https://git.iws.uni-stuttgart.de/dumux-pub/jaust2020a.

TODO list

• Cleanup/optimization of test routine
  • Currently the CMakeLists.txt uses an unsafe way to add DuMuX Python-scripts to PYTHONPATH. I should use the proper environment variable pointing to the dumux directory (of which I forgot the name). Has to be done later
  • I have a separate tests for the Darcy and the FreeFlow domain. This leads to the solver being called twice. Ideally I would call the solvers only once and afterwards check the vtu files.
    • Solved by means of the already existing comparison script which supports comparing several VTU-files at the same time.
• Set up tests for -> Done for relevant cases
  • Iterative reverse coupling,
  • Monolithic coupling
• Upgrading to newer DuMuX version
  • DuMuX 3.3, we directly aim for DuMuX 3.4git -> Currently depends on the other PR
• Upgrading to newer preCICE version (2.X) (see also https://git.iws.uni-stuttgart.de/dumux-appl/dumux-precice~/-/merge_requests/5) This will be done, but not for the dumux-pub module
  • preCICE 2.2.0 Note I did some intermediate porting, but the results look quite different.
• Moving into pub module -> Code has been transferred to https://git.iws.uni-stuttgart.de/dumux-pub/jaust2020a (just needs to be made public)
• Define a compile time constant to switch between correct and wrong velocity reconstruction in monolithic case Postponed As it was needed for FVCA results

Notes

• I made the tests dependent on each other. This allows to call the tests with ctest -j NJOBS where NJOBS is larger than one. Otherwise the tests may fail as the preCICE initialization relies on some files written in the directory the test is run in. This depedendency could be removed if each test would run in a separate subdirectory.