[DO-NOT-MERGE] Test kaniko improvements

[balopat]

testing #1426 - it is not obvious for me why it's failing on kokoro.

[googlebot]

So there's good news and bad news.

👍 The good news is that everyone that needs to sign a CLA (the pull request submitter and all commit authors) have done so. Everything is all good there.

😕 The bad news is that it appears that one or more commits were authored or co-authored by someone other than the pull request submitter. We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that here in the pull request.

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[codecov-io]

Codecov Report

Merging #1427 into master will increase coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #1427      +/-   ##
=========================================
+ Coverage   44.77%   44.8%   +0.02%     
=========================================
  Files         111     111              
  Lines        4554    4551       -3     
=========================================
  Hits         2039    2039              
+ Misses       2310    2307       -3     
  Partials      205     205

Impacted Files	Coverage Δ
pkg/skaffold/build/kaniko/run.go	0% <0%> (ø)	⬆️
pkg/skaffold/build/kaniko/kaniko.go	0% <0%> (ø)	⬆️

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