fix: modified UniformAcrossAzUpdateStrategy update strategy to be as expected

[ccpeng]

fixes: https://github.com/keikoproj/upgrade-manager/issues/349

the README has a broken link to uniform_across_az_update_strategy.yaml but I think this is the intended behavior

[codecov[bot]]

Codecov Report

Merging #395 (70a18e2) into master (84dd4a7) will not change coverage. The diff coverage is 70.58%.

@@           Coverage Diff           @@
##           master     #395   +/-   ##
=======================================
  Coverage   39.09%   39.09%           
=======================================
  Files           7        7           
  Lines         931      931           
=======================================
  Hits          364      364           
  Misses        540      540           
  Partials       27       27           

Flag	Coverage Δ
unittests	39.09% <70.58%> (ø)

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Files	Coverage Δ
controllers/upgrade.go	46.21% <70.58%> (ø)

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[ZihanJiang96]

LGTM