Add error codes for structure test failures

[PriyaModali]

Fixes: #5384

Description
Adding error codes for test failures

User facing changes
These changes will enable Skaffold dev to return distinct error codes when tests fail.

There are no visible user facing changes.

Related:
#5333

[codecov]

Codecov Report

Merging #5385 (ea56a7f) into master (0ba3ee7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5385   +/-   ##
=======================================
  Coverage   71.55%   71.56%           
=======================================
  Files         395      397    +2     
  Lines       14409    14427   +18     
=======================================
+ Hits        10310    10324   +14     
- Misses       3333     3335    +2     
- Partials      766      768    +2     

Impacted Files	Coverage Δ
pkg/skaffold/test/error.go	100.00% <100.00%> (ø)
pkg/skaffold/test/structure/error.go	100.00% <100.00%> (ø)
pkg/skaffold/test/structure/structure.go	100.00% <100.00%> (ø)
pkg/skaffold/test/test.go	86.79% <100.00%> (ø)
pkg/skaffold/util/tar.go	50.66% <0.00%> (-5.34%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0ba3ee7...ea56a7f. Read the comment docs.