AV-2079: Fix cloudstorage to handle empty strings in config

[Zharktas]

literal_eval doesn't cope with empty string, lets be coherent with our config.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6761069) 23.46% compared to head (bbc073a) 23.43%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2097      +/-   ##
==========================================
- Coverage   23.46%   23.43%   -0.04%     
==========================================
  Files          43       43              
  Lines        6030     6038       +8     
  Branches       34       34              
==========================================
  Hits         1415     1415              
- Misses       4615     4623       +8     

Flag	Coverage Δ
cdk	93.13% <ø> (ø)
ckan	17.99% <ø> (-0.03%)	⬇️

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see 3 files with indirect coverage changes

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