[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/config/utils.py

@@ -0,0 +1,95 @@
+import logging
+import os
+import socket
+from contextlib import contextmanager
+from typing import Optional
+
+import psutil
+
+# import torch.distributed as dist
+
+
+@contextmanager
+def temp_env(env_dict):
+    old_env = {}
+    for k, v in env_dict.items():
+        old_env[k] = os.environ.get(k)
+        os.environ[k] = str(v)
+    try:
+        yield
+    finally:
+        for k, v in old_env.items():
+            if v is None:
+                os.environ.pop(k, None)
+            else:
+                os.environ[k] = v
+
+
+# @contextmanager
+# def dist_group(backend="gloo"):
+#     if dist.is_initialized():
+#         yield
+#         return
+
+#     dist.init_process_group(backend=backend)
+#     try:
+#         yield
+#     finally:
+#         dist.destroy_process_group()
+
+
+def get_cluster_ips(word_size: int = 2) -> list[str]:
+    """
+    Returns the IP addresses of all nodes in the cluster.
+    0: leader
+    1~N-1: workers
+    """
+    leader_dns = os.getenv("LWS_LEADER_ADDRESS")
+    if not leader_dns:
+        raise RuntimeError("LWS_LEADER_ADDRESS is not set")
+    cluster_dns = [leader_dns]
+    for i in range(1, word_size):
+        cur_dns = f"vllm-0-{i}.vllm.vllm-project"
+        cluster_dns.append(cur_dns)
+    return [socket.gethostbyname(dns) for dns in cluster_dns]
+
+
+def get_avaliable_port(start_port: int = 6000, end_port: int = 7000) -> int:
+    import socket
+    for port in range(start_port, end_port):
+        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+            try:
+                s.bind(("", port))
+                return port
+            except OSError:
+                continue
+    raise RuntimeError("No available port found")
+
+
+def get_cur_ip() -> str:
+    """Returns the current machine's IP address."""
+    return socket.gethostbyname_ex(socket.gethostname())[2][0]
+
+
+def get_net_interface(ip: Optional[str] = None) -> Optional[str]:
+    """
+    Returns specified IP's inetwork interface.
+    If no IP is provided, uses the first from hostname -I.
+    """
+    if ip is None:
+        ip = get_cur_ip()
+
+    for iface, addrs in psutil.net_if_addrs().items():
+        for addr in addrs:
+            if addr.family == socket.AF_INET and addr.address == ip:
+                return iface
+    return None
+
+
+def setup_logger():
+    """Setup logging configuration."""
+    logging.basicConfig(
+        level=logging.INFO,
+        format="[%(asctime)s] [%(levelname)s] %(message)s",
+        datefmt="%Y-%m-%d %H:%M:%S",
+    )