AbacusHOD: Moving mock dir creation to run_hod

[SBouchard01]

If mkdir is called in staging, it creates empty directories all over the place when running AbacusHOD on the fly (which I have to do as the amount of BGS mocks I create is too big to keep on disk)

I moved it to run_hod and added a condition on write_to_disk to ensure empty folders are not created.

Also, I added two FileNotFoundError in staging because the errors raised in those case were not really understandable ( e.g. an IndexError)

Overall behavior should in theory be unchanged 👍🏼

[lgarrison]

Thanks @SBouchard01! I agree we should fix this. Do you think we could just move the mkdir call to inside gen_gal_cat()? That way it will work if someone calls gen_gal_cat directly. I think that's the only routine that writes to mock_dir.

[SBouchard01]

From what I see we could even remove it, as gen_gal_cat already has a safety feature to ensure the directory is created. (and it seems the only place where mock_dir/savedir is used in that function)

[lgarrison]

Good point. Thanks again!