Metadata in mock catalog files? #30

From #28 (comment):

One small thing I noticed while looking at the tests is that the ELG.dat and LRG.dat files don't flag that they came from halo light cones. In fact, they don't contain any simulation or cosmology information, just the HOD parameter information (Acen, Asat, etc). I've kind of lost track of what file format we're using to distribute AbacusSummit mocks, but we might want to check that we are echoing the simulation/cosmology information to those files. Maybe we're already doing that though, just not in the tests; @SandyYuan, do you know?