[test][freeflow] Use Dumux::initialize

test/freeflow/navierstokes/angeli/main.cc

test/freeflow/navierstokes/channel/1d/main.cc

test/freeflow/navierstokes/channel/2d/main.cc

test/freeflow/navierstokes/channel/3d/main.cc

test/freeflow/navierstokes/channel/pipe/main.cc

test/freeflow/navierstokes/donea/main.cc

test/freeflow/navierstokes/donea/main_momentum.cc

test/freeflow/navierstokes/kovasznay/main.cc

test/freeflow/navierstokes/periodic/main.cc

test/freeflow/navierstokes/sincos/main.cc

test/freeflow/navierstokesnc/channel/main.cc

test/freeflow/navierstokesnc/densitydrivenflow/main.cc

test/freeflow/navierstokesnc/maxwellstefan/main.cc

test/freeflow/rans/main.cc

test/freeflow/ransnc/main.cc

test/freeflow/shallowwater/bowl/main.cc

test/freeflow/shallowwater/dambreak/main.cc

test/freeflow/shallowwater/poiseuilleflow/main.cc

test/freeflow/shallowwater/roughchannel/main.cc