fix(e2e): Add cleanup trap to prevent false positives in CI test runs

[fjglira]

The e2e test script was storing the Ginkgo exit code but could still exit unexpectedly before cleanup, causing CI to mark incomplete test runs as successful (false positives).

What type of PR is this?

• Enhancement / New Feature
• Bug Fix
• Refactor
• Optimization
• Test
• Documentation Update

What this PR does / why we need it:

Problem:
The e2e test script was storing the Ginkgo exit code, but could still exit unexpectedly before cleanup, causing CI to mark incomplete test runs as successful (false positives).

Solution:

• Added a cleanup() function with trap cleanup EXIT INT TERM to ensure uninstall always runs
• Moved cleanup logic to the trap so it executes on normal exit, interrupts, and terminations
• Simplified the main flow to immediately exit with the captured Ginkgo exit code
• Cleanup errors are suppressed to preserve the original test result

Result:

• CI now correctly reflects test failures and interruptions
• JUnit reports are still generated and cleanup always occurs
• No more false positive test results from incomplete runs

Which issue(s) this PR fixes:

Fixes #1226

Related Issue/PR #

Additional information:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.54%. Comparing base (749d908) to head (3bbde83).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1227      +/-   ##
==========================================
+ Coverage   77.39%   77.54%   +0.14%     
==========================================
  Files          44       44              
  Lines        2823     2823              
==========================================
+ Hits         2185     2189       +4     
+ Misses        529      526       -3     
+ Partials      109      108       -1     

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[ctartici]

lgtm

[istio-testing]

In response to a cherrypick label: new pull request created: #1232