[CI/Build] Use FileStore for DeepEP test rendezvous (#56595)

Signed-off-by: Kevin Luu <51931015+khluu@users.noreply.github.com>
Co-authored-by: OpenAI Codex <codex@openai.com>

tests/kernels/moe/parallel_utils.py

@@ -3,7 +3,6 @@
 """DeepEP test utilities."""
 
 import dataclasses
-import os
 import traceback
 from collections.abc import Callable
 from typing import Concatenate
@@ -14,7 +13,7 @@ from torch.multiprocessing import spawn  # pyright: ignore[reportPrivateImportUs
 from typing_extensions import ParamSpec
 
 from vllm.utils.import_utils import has_deep_ep, has_deep_ep_v2
-from vllm.utils.network_utils import get_open_port
+from vllm.utils.network_utils import get_file_store_init_method
 
 if has_deep_ep():
     from vllm.model_executor.layers.fused_moe.prepare_finalize.deepep_ht import (
@@ -105,7 +104,7 @@ def parallel_launch(
                 world_size,
                 world_size,
                 0,
-                f"tcp://{os.getenv('LOCALHOST', 'localhost')}:{get_open_port()}",
+                get_file_store_init_method(),
                 worker,
             )
             + args,