Fortran error tests

Fortran error tests should be added, as suggested in #13 (closed).

For this some things have to be reworked, additional error checking enabled (such as correct permissions for already existing VTK output directories), that we can use to test against.

tests/fortran_error/CMakeLists.txt

 # The VTK error test case, where the output directory is not accessible.
+include(FindUnixCommands)
 set(OUT_DIR vtk_outline)
 add_test(
     NAME fortran_error_vtk_setup