Fix various metadata bugs in 'awips_tiled' writer

[djhoese]

Closes ssec/polar2grid#417

Kathy (@kathys) has been doing some testing and it looks like there were a couple metadata related issues with the AWIPS tiles being produced by this writer. Most of these are from past refactors and incomplete tests not catching them.

• Closes #xxxx
• Tests added

[codecov]

Codecov Report

Merging #2032 (21b4756) into main (5ed7871) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2032   +/-   ##
=======================================
  Coverage   93.65%   93.65%           
=======================================
  Files         282      282           
  Lines       41875    41865   -10     
=======================================
- Hits        39217    39209    -8     
+ Misses       2658     2656    -2     

Flag	Coverage Δ
behaviourtests	4.76% <0.00%> (+<0.01%)	⬆️
unittests	94.18% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
satpy/tests/writer_tests/test_awips_tiled.py	99.04% <100.00%> (+0.57%)	⬆️
satpy/writers/awips_tiled.py	84.04% <100.00%> (+0.03%)	⬆️

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[djhoese]

Just committed a blank commit to see if codefactor was happy after a bug fix on their side but as I pushed it I realized it was already passing. Oops.

[coveralls]

Coverage increased (+0.003%) to 94.114% when pulling 21b4756 on djhoese:bugfix-awips-tiled into 5ed7871 on pytroll:main.

[djhoese]

CC @joleenf

We have confirmation from Lee Cronce at SSEC that the files produced with these changes now load successfully and look as expected. I'll merge this in a little bit.

[djhoese]

Given the size of these changes and that I'm the only one of the core developers familiar with this writer, I'm just going to merge it. If it is decided that this should have had a review then let's define that somewhere.