epp: add more error integration test cases

[zhengkezhou1]

Fix #325

Add test cases for:

• handling unavailable backend pods
• invalid model requests

[k8s-ci-robot]

Hi @zhengkezhou1. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[ahg-g]

/ok-to-test

[zhengkezhou1]

@liu-cong can your please take a look?

[kfswain]

/lgtm
/approve

Looks great! Thanks!

Quick question; why the giraffe hate? 😆

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kfswain, zhengkezhou1

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[zhengkezhou1]

/lgtm /approve

Looks great! Thanks!

Quick question; why the giraffe hate? 😆

Its Meme: https://www.reddit.com/r/funny/comments/qog3f/giraffes_are_heartless_creatures/?utm_source=share&utm_medium=mweb3x&utm_name=mweb3xcss&utm_term=1&utm_content=share_button

[kfswain]

hahaha I love it