[Test] Unify L2/L3 test layout, Buildkite steps, and test helpers (#2556)

Signed-off-by: wangyu <410167048@qq.com>
Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Signed-off-by: wangyu <53896905+yenuo26@users.noreply.github.com>
Co-authored-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>

tests/entrypoints/test_utils.py

@@ -328,7 +328,7 @@ class TestResolveModelConfigPath:
         )
         mocker.patch(
             "vllm_omni.entrypoints.utils.current_omni_platform.get_default_stage_config_path",
-            return_value="vllm_omni/model_executor/stage_configs",
+            return_value="vllm_omni/deploy",
         )
 
         original_exists = os.path.exists