[CI] fix the teardown output of disaggregation test (#19193)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

python/sglang/test/test_utils.py

@@ -546,21 +546,21 @@ def try_cached_model(model_repo: str):
     return model_dir if model_dir else model_repo
 
 
-def popen_with_error_check(command: list[str], allow_exit: bool = False):
-    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+def popen_with_error_check(command: list[str]):
+    process = subprocess.Popen(command, stdout=None, stderr=None)
 
     def _run_and_check():
-        stdout, stderr = process.communicate()
+        process.wait()
 
-        while process.poll() is None:
-            time.sleep(5)
+        if process.returncode == -9:
+            return
 
-        if not allow_exit or process.returncode != 0:
+        if process.returncode != 0:
             raise Exception(
-                f"{command} exited with code {process.returncode}\n{stdout=}\n{stderr=}"
+                f"{shlex.join(command)} exited with code {process.returncode}"
             )
 
-    t = threading.Thread(target=_run_and_check)
+    t = threading.Thread(target=_run_and_check, daemon=True)
     t.start()
     return process