Fix pygrib openfiles

[adybbroe]

• Closes #xxxx
• Tests added
• Tests passed: Passes pytest pyspectral
• Passes flake8 pyspectral
• Fully documented

[mraspaud]

Looks like this code needs some TLC, but this is good enough for now I guess.
Do we really need all these new debug messages?
Also, let's make a function for getting a temporary filename.

[codecov]

Codecov Report

Merging #20 (5ad39b9) into master (201454a) will decrease coverage by 0.07%.
The diff coverage is 9.52%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
- Coverage   27.87%   27.80%   -0.08%     
==========================================
  Files          11       11              
  Lines        1693     1705      +12     
==========================================
+ Hits          472      474       +2     
- Misses       1221     1231      +10     

Flag	Coverage Δ
unittests	27.80% <9.52%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
nwcsafpps_runner/prepare_nwp.py	0.00% <0.00%> (ø)
nwcsafpps_runner/utils.py	26.84% <100.00%> (+0.38%)	⬆️

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[mraspaud]

LGTM, feel free to merge once the tests pass.

[adybbroe]

Thanks @mraspaud
I think it will fail on Ubuntu-latest. Something with gdal-config. I couldn't really see what I could do to make it pass, so I left it for now. Already a good step forward to have testing on github I thought.

[adybbroe]

Oh, it also fails on Windows, as I have hardcoded Linux style filepaths in the tests. The code had never run under Windows yet, as far as we know, so I will ignore this here, and address it in a separate PR