adapt test_diffusion3d such that it also accepts parameters from the comman...

adapt test_diffusion3d such that it also accepts parameters from the comman line in the usual way. This should make the CMake test work.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11491 2fb0f335-1f38-0410-981e-8018bf24f1b0