Make test_utils.py use pipes to avoid file access conflicts on Windows (#9072)

Co-authored-by: Mehrdad <noreply@github.com>

python/ray/serve/tests/test_persistence.py

@@ -1,8 +1,5 @@
-import os
-import subprocess
-import tempfile
-
 import ray
+import ray.test_utils
 from ray import serve
 
 
@@ -20,20 +17,11 @@ def driver(flask_request):
 serve.create_backend("driver", driver)
 serve.create_endpoint("driver", backend="driver", route="/driver")
 """.format(ray.worker._global_node._redis_address)
-
-    with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
-        path = f.name
-        f.write(script)
-
-    proc = subprocess.Popen(["python", path])
-    return_code = proc.wait(timeout=10)
-    assert return_code == 0
+    ray.test_utils.run_string_as_driver(script)
 
     handle = serve.get_handle("driver")
     assert ray.get(handle.remote()) == "OK!"
 
-    os.remove(path)
-
 
 if __name__ == "__main__":
     import sys