[CI] Refator multi-node CI (#3487)

### What this PR does / why we need it?
Refactor the multi-machine CI use case. The purpose of this PR is to
increase the ease of adding multi-machine CI use cases, allowing
developers to add multi-machine cluster model testing use cases
(including PD separation) by simply adding a new YAML configuration
file.
### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0

---------

Signed-off-by: wangli <wangli858794774@gmail.com>

tests/e2e/nightly/multi_node/test_multi_node.py

@@ -0,0 +1,30 @@
+from tests.e2e.conftest import RemoteOpenAIServer
+from tests.e2e.nightly.multi_node.config.multi_node_config import (
+    DISAGGREGATED_PREFILL_PROXY_SCRIPT, MultiNodeConfig)
+
+
+def test_multi_node() -> None:
+    config = MultiNodeConfig.from_yaml()
+    env_dict = config.envs
+    # perf_cmd = config.perf_cmd
+    # acc_cmd = config.acc_cmd
+    server_port = config.server_port if not config.disaggregated_prefill else config.proxy_port
+    server_host = config.cluster_ips[0]
+    with config.launch_server_proxy(DISAGGREGATED_PREFILL_PROXY_SCRIPT):
+        with RemoteOpenAIServer(
+                model=config.model,
+                vllm_serve_args=config.server_cmd,
+                server_port=server_port,
+                server_host=server_host,
+                env_dict=env_dict,
+                auto_port=False,
+                max_wait_seconds=2000,
+        ) as remote_server:
+            # base_url = remote_server.url_root
+            if config.is_master:
+                pass
+                # TODO: enable perf and acc test
+                # subprocess.run(perf_cmd, check=True)
+                # subprocess.run(acc_cmd, check=True)
+            else:
+                remote_server.hang_until_terminated()