fix vllm template (#813)

# What does this PR do?

- Fix vLLM template to resolve
https://github.com/meta-llama/llama-stack/issues/805
- Fix agents test with shields

## Test Plan

```
vllm serve meta-llama/Llama-3.1-8B-Instruct
VLLM_URL="http://localhost:8000/v1" INFERENCE_MODEL="meta-llama/Llama-3.1-8B-Instruct" llama stack run ./llama_stack/templates/remote-vllm/run.yaml
```

```
LLAMA_STACK_BASE_URL=http://localhost:8321 pytest -v ./tests/client-sdk/
```

<img width="1245" alt="image"
src="https://github.com/user-attachments/assets/9af27684-5a9c-4187-b338-cbfc5211bd99"
/>


- custom tool flaky due to model outputs
- /completions API not implemented

**Vision Model**
- 11B-Vision-Instruct
<img width="1240" alt="image"
src="https://github.com/user-attachments/assets/1d3b3b17-fa09-43a7-b56c-3f77263825c5"
/>


## Sources

Please link relevant resources if necessary.


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [ ] Ran pre-commit to handle lint / formatting issues.
- [ ] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

tests/client-sdk/agents/test_agents.py

@@ -182,7 +182,8 @@ def test_builtin_tool_web_search(llama_stack_client, agent_config):
     assert "tool_execution>" in logs_str
     assert "Tool:brave_search Response:" in logs_str
     assert "mark zuckerberg" in logs_str.lower()
-    assert "No Violation" in logs_str
+    if len(agent_config["output_shields"]) > 0:
+        assert "No Violation" in logs_str
 
 
 def test_builtin_tool_code_execution(llama_stack_client, agent_config):