Fix not generating tax rate id in all cases, implement testing replac…

[davidweterings]

Fix not generating tax rate id in all cases, implement testing replaceTaxRate action

[codecov]

Codecov Report

Merging #42 into master will decrease coverage by <.01%.
The diff coverage is 64.28%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
- Coverage   74.79%   74.79%   -0.01%     
==========================================
  Files         138      138              
  Lines       21892    21905      +13     
==========================================
+ Hits        16375    16383       +8     
- Misses       5517     5522       +5

Impacted Files	Coverage Δ
src/commercetools/testing/utils.py	63.41% <33.33%> (-1.59%)	⬇️
src/commercetools/testing/tax_categories.py	83.33% <72.72%> (-3.77%)	⬇️

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