Fix EnsureCleanup to properly skip clean up when requested

[dprotaso]

EnsureCleanup is called after creating some resource to
register clean up handlers. No invocation of this function
uses defer so typically the test has not failed. When passing
in the SkipCleanupOnFail=true flag we were then never skipping
said cleanup because of it.

[knative-prow]

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[dprotaso]

Looks like the change was introduced in #15217
/assign @mgencur
/assign @linkvt

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.21%. Comparing base (2cd582b) to head (20b72e7).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16372      +/-   ##
==========================================
+ Coverage   80.18%   80.21%   +0.02%     
==========================================
  Files         216      216              
  Lines       13440    13440              
==========================================
+ Hits        10777    10781       +4     
+ Misses       2298     2295       -3     
+ Partials      365      364       -1     

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[dprotaso]

@mgencur your comment in your PR said

Fix a bug related to ServingFlags.SkipCleanupOnFail. The cleanup should really be skipped only if the test fails. This was missed during reviews on the #12482

I think this is accurate - let me tweak what I did

[dprotaso]

/retest

[linkvt]

/lgtm
/hold for Martins review

[mgencur]

/lgtm

[mgencur]

/unhold