[rans] Fix compiling and add wall distance

dumux/freeflow/navierstokes/staggered/localresidual.hh

dumux/freeflow/rans/CMakeLists.txt

dumux/freeflow/rans/model.hh

dumux/freeflow/rans/problem.hh

dumux/freeflow/rans/volumevariables.hh

dumux/freeflow/rans/vtkoutputfields.hh

dumux/freeflow/rans/zeroeq/CMakeLists.txt

dumux/freeflow/rans/zeroeq/indices.hh

dumux/freeflow/rans/zeroeq/model.hh

dumux/freeflow/rans/zeroeq/volumevariables.hh

test/freeflow/rans/pipelauferproblem.hh

test/freeflow/rans/test_pipe_laufer.cc