propagate fiberassign HDU0 keywords too

[sbailey]

This PR fixes #1076 where some fiberassign header keywords were not propagated into the fibermap files, thus losing some of the fiber assignment input provenance. The problem was that we were propagating keywords from the 'FIBERASSIGN' HDU, but not additional keywords from HDU 0 of the fiberassign files. Now assemble_fibermap propagates keywords from both HDUs into the fibermap file (along with keywords from the raw data).

Keywords that were previously missing that are now included when running assemble_fibermap -n 20201215 -e 68065 -o fm-2.fits:

GFA       /global/cfs/cdirs/desi/target/catalogs/dr9/0.47.0/gfas
SKY       /global/cfs/cdirs/desi/target/catalogs/dr9/0.47.0/skies
SKYSUPP   /global/cfs/cdirs/desi/target/catalogs/gaiadr2/0.47.0/skies-supp
TARG      /global/cfs/cdirs/desi/target/catalogs/dr9/0.47.0/targets/sv1/resolve/dark/
FAFLAVOR  cmxlrgqso
FAOUTDIR  /global/cfs/cdirs/desi/users/raichoor/desi-sv1-20201212/
RUNDATE   2020-03-06T00:00:00
OBSCON    DARK|GRAY|BRIGHT

Full disclosure: I renamed the generic "OUTDIR" to "FAOUTDIR" to dis-ambiguate it with other potential output directories. I am slightly tempted to do that for the other input directory keywords too to avoid downstream conflicts in the future.

@moustakas if you happen to see this in time, there is a brief window of opportunity to inspect and comment before we start making tags for Cascades. Example files in /global/cfs/cdirs/desi/users/sjbailey/spectro/redux/test:

• original : fm-1.fits
• new: fm-2.fits

[sbailey]

@weaverba137 python setup.py build_sphinx works locally (sphinx v3.1.2) but has started to fail on GitHub Actions doc tests. Could you investigate? I won't let that be a blocking factor for merging PRs so this isn't super-urgent, but it would be nice to get this addressed sooner than later to avoid false failure flags.

[coveralls]

Coverage decreased (-0.005%) to 28.97% when pulling b3366e2 on fibermap_keywords into a9c55b1 on master.

[moustakas]

This looks great, thanks.

[weaverba137]

I've heard that the latest version of Sphinx has some problems. Pinning Sphinx<3.5 should fix it, but I'll have to test tomorrow.