chore: standardize nodeSelectors

[jackfrancis]

Reason for Change:

Standardizes nodeSelector

Issue Fixed:

Fixes #3351

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3406 into master will increase coverage by 0.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3406      +/-   ##
==========================================
+ Coverage   73.07%   73.17%   +0.10%     
==========================================
  Files         147      147              
  Lines       24945    24923      -22     
==========================================
+ Hits        18229    18238       +9     
+ Misses       5588     5559      -29     
+ Partials     1128     1126       -2     

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	54.08% <ø> (+0.87%)	⬆️
pkg/engine/artifacts.go	99.12% <0.00%> (-0.88%)	⬇️
pkg/api/vlabs/types.go	73.30% <0.00%> (ø)
pkg/api/types.go	94.37% <0.00%> (+0.02%)	⬆️
pkg/engine/virtualmachinescalesets.go	81.28% <0.00%> (+0.09%)	⬆️
pkg/engine/virtualmachines.go	80.98% <0.00%> (+0.13%)	⬆️
pkg/api/convertertoapi.go	93.50% <0.00%> (+0.33%)	⬆️
pkg/api/converterfromapi.go	94.01% <0.00%> (+0.36%)	⬆️

---

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma

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