Throw error and exit if config file isn't readable

[yuvipanda]

Fixes #73

[cisaacstern]

Thanks for this @yuvipanda! Looks like the tweak in 502735b was all we needed to get it to work 😄 .

Sort of an https://github.com/yuvipanda/opposite-day situation! 😆

[cisaacstern]

Hmm I spoke too soon... now we have errors if the default config is not found...

'Could not read config from file pangeo_forge_runner_config.py. Make sure it exists and is readable\n'

🤔

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03% 🎉

Comparison is base (ce14ad5) 95.75% compared to head (fd77b7d) 95.79%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #88      +/-   ##
==========================================
+ Coverage   95.75%   95.79%   +0.03%     
==========================================
  Files          13       13              
  Lines         424      428       +4     
==========================================
+ Hits          406      410       +4     
  Misses         18       18              

Files Changed	Coverage Δ
pangeo_forge_runner/commands/base.py	98.48% <100.00%> (+0.09%)	⬆️

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[cisaacstern]

Merging this as a big step forward but opened #100 to address remaining corner cases.