tests not cleaning up after themselves

[dmehring]

These downloaded files are left after running python -m pytest tests/unit/ -v --tb=short

drwxrwxr-x  3 dmehring dmehring 4096 Apr  7 10:21 Antennae_fld1_casa_lsrk.ps.zarr
drwxrwxr-x  4 dmehring dmehring 4096 Apr  7 10:23 test_hogbom_resid.im
drwxrwxr-x  4 dmehring dmehring 4096 Apr  7 10:23 refim_point_im.residual
drwxrwxr-x  3 dmehring dmehring 4096 Apr  7 10:23 test_hogbom_psf.im
drwxrwxr-x  3 dmehring dmehring 4096 Apr  7 10:23 refim_point_im.psf

Please have tests clean up after themselves.