[1/N] Refactor nightly test structure (#5479)

### What this PR does / why we need it?
This patch is a series of refactoring actions, including clarifying the
directory structure of nightly tests, refactoring the config retrieval
logic, and optimizing the workflow, etc. This is the first step:
refactoring the directory structure of nightly to make it more readable
and logical.

- vLLM version: v0.13.0
- vLLM main:
5326c89803

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

tests/e2e/nightly/multi_node/scripts/utils.py

@@ -0,0 +1,149 @@
+import logging
+import os
+import socket
+import time
+from contextlib import contextmanager
+from typing import List, Optional
+
+import psutil
+
+DISAGGEGATED_PREFILL_PORT = 5333
+CONFIG_BASE_PATH = "tests/e2e/nightly/multi_node/config/"
+DEFAULT_SERVER_PORT = 8080
+
+
+@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
+
+
+def dns_resolver(retries: int = 240, base_delay: float = 0.5):
+    # We should resolve DNS with retries to avoid transient network issues.
+    # When the pod is just started, DNS resolution may fail.
+    def resolve(dns: str):
+        delay = base_delay
+        for attempt in range(retries):
+            try:
+                return socket.gethostbyname(dns)
+            except socket.gaierror:
+                if attempt == retries - 1:
+                    raise
+                time.sleep(delay)
+                delay = min(delay * 1.5, 5)
+
+    return resolve
+
+
+def get_cluster_dns_list(world_size: int) -> List[str]:
+    if world_size < 1:
+        raise ValueError(f"world_size must be >= 1, got {world_size}")
+
+    leader_dns = os.getenv("LWS_LEADER_ADDRESS")
+    if not leader_dns:
+        raise RuntimeError(
+            "environment variable LWS_LEADER_ADDRESS is not set")
+
+    # Expected format:
+    # <leader-name>.<group-name>.<namespace>
+    parts = leader_dns.split(".")
+    if len(parts) < 3:
+        raise ValueError(f"invalid leader DNS format: {leader_dns}")
+
+    leader_name, group_name, namespace = parts[0], parts[1], parts[2]
+
+    worker_dns_list = [
+        f"{leader_name}-{idx}.{group_name}.{namespace}"
+        for idx in range(1, world_size)
+    ]
+
+    return [leader_dns, *worker_dns_list]
+
+
+def get_cluster_ips(word_size: int = 2) -> list[str]:
+    resolver = dns_resolver()
+    return [resolver(dns) for dns in get_cluster_dns_list(word_size)]
+
+
+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(retries: int = 20, base_delay: float = 0.5):
+    """
+    Returns the pod/machine's primary IP address with retry.
+    This is necessary because network interfaces may not be ready
+    immediately after container startup.
+    """
+    delay = base_delay
+
+    for attempt in range(retries):
+        try:
+            # Best method: UDP trick (doesn't actually send packets)
+            with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
+                s.connect(("8.8.8.8", 80))
+                return s.getsockname()[0]
+        except Exception:
+            # fallback: hostname resolution
+            try:
+                return socket.gethostbyname(socket.gethostname())
+            except Exception:
+                if attempt == retries - 1:
+                    raise RuntimeError("Failed to determine local IP address")
+                time.sleep(delay)
+                delay = min(delay * 1.5, 5)
+
+
+def get_net_interface(ip: Optional[str] = None) -> 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
+    raise RuntimeError(f"No network interface found for IP {ip}")
+
+
+def get_all_ipv4():
+    """get all the ipv4 address for current node"""
+    ipv4s = set()
+    hostname = socket.gethostname()
+
+    for info in socket.getaddrinfo(hostname, None, family=socket.AF_INET):
+        ipv4s.add(info[4][0])
+
+    ipv4s.add("127.0.0.1")
+
+    return list(ipv4s)
+
+
+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",
+    )