[Python tests] Allow passing kwargs to grpc.server in test_server (#36455)

Allow passing `kwargs` to `grpc.server` in test server.

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Closes #36455

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36455 from XuanWang-Amos:disable_reflection_in_tests d9a7e3d7fa
PiperOrigin-RevId: 629149234

src/python/grpcio_tests/tests/unit/test_common.py

@@ -13,8 +13,10 @@
 # limitations under the License.
 """Common code used throughout tests of gRPC."""
 
+import ast
 import collections
 from concurrent import futures
+import os
 import threading
 
 import grpc
@@ -110,9 +112,12 @@ def test_server(max_workers=10, reuse_port=False):
 
     These servers have SO_REUSEPORT disabled to prevent cross-talk.
     """
+    server_kwargs = os.environ.get("GRPC_ADDITIONAL_SERVER_KWARGS", "{}")
+    server_kwargs = ast.literal_eval(server_kwargs)
     return grpc.server(
         futures.ThreadPoolExecutor(max_workers=max_workers),
         options=(("grpc.so_reuseport", int(reuse_port)),),
+        **server_kwargs,
     )