fixed 2p test: density for initial/BC had been hardcoded for one specific...

fixed 2p test: density for initial/BC had been hardcoded for one specific FluidSystem, it is now general, because c6834 motivated usage with several FluidSystems.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@7114 2fb0f335-1f38-0410-981e-8018bf24f1b0