[Test Framework] Fix apps forwarder port

[nmittler]

Was using the service port, but should have been using the target port.

Fixes #13091

[istio-testing]

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[istio-testing]

@nmittler: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
prow/istio-pilot-multicluster-e2e.sh	48f1d10	link	/test istio-pilot-multicluster-e2e

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[stale]

This pull request has been automatically marked as stale because it has not had activity in the last 2 weeks. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!

[ozevren]

I don't remember seeing this PR, I missed this. Is it still relevant?

[nmittler]

@ozevren I'm about to replace apps with echo now, so I'll just close this out at that point.

[nmittler]

No longer applies, since apps has been replaced by Echo. Closing.