test: fix flaky sample test

[laljikanjareeya]

It seems that if an instance is old enough, the operations' logs "disappear". Hence return undefined in the test logic.

Propose implementation:
Instead of relying on the operation, we added another label with the timestamp of instance creation and validate the age of the instance based on that label.

Another point towards this implementation is that similar logic is used in system-test clean up.

Fixes #1322

[codecov]

Codecov Report

Merging #1325 (61782b6) into master (ffb88bb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master    #1325    +/-   ##
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  Coverage   98.60%   98.60%            
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  Files          23       23            
  Lines       21899    21899            
  Branches     1099     1225   +126     
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  Hits        21593    21593            
  Misses        297      297            
  Partials        9        9            

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[AVaksman]

LGTM

[AVaksman]

I have come across the same issue before. It seems that if an instance is old enough, the operations' logs "disappear".
Hence return undefined in the test logic.
This approach seems fine. Instead of relying on the operation, we add another label with the timestamp of instance creation and validate the age of the instance based on that label.

Another point towards this implementation is that similar logic is used in system-test clean up.