[e2e] Append an ending message in the test output

[tnqn]

To differentiate whether the output gets cut or the agnhost command didn't output anything.

For #5139

[tnqn]

I haven't figured out why but none of the NetworkPolicy have ever failed a single time in 15 runs after appending a message to the end of the result. Perhaps this somehow fixes the underlying issue in the clientset lib?
Promote the PR as an official PR as suggested by @antoninbas
cc @Dyanngg @GraysonWu

[antoninbas]

It's fine to merge it IMO, even if we don't really understand why it helps. What matters here is to reduce / eliminate the flakiness. We can keep track of test failures over time and see what happens.

Really strange that we only see failures in TestGroupNoK8sNP, when all NP tests are pretty much built the same way and use the same functions.

[Dyanngg]

Really strange that we only see failures in TestGroupNoK8sNP, when all NP tests are pretty much built the same way and use the same functions.

This is because TestGroupNoK8sNP has 60 tests in it while there are only around 5 other cases that test traffic outside of this test group

[antoninbas]

Really strange that we only see failures in TestGroupNoK8sNP, when all NP tests are pretty much built the same way and use the same functions.

This is because TestGroupNoK8sNP has 60 tests in it while there are only around 5 other cases that test traffic outside of this test group

Makes sense

[tnqn]

/test-e2e
/skip-conformance
/skip-networkpolicy