Don't load manual benchmark as test

src/python/grpcio_tests/tests/stress/unary_stream_benchmark.py

@@ -1,16 +1,3 @@
-# Copyright 2019 The gRPC authors.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
 import datetime
 import threading
 import grpc
@@ -22,9 +9,6 @@ import contextlib
 try:
     from src.python.grpcio_tests.tests.stress import unary_stream_benchmark_pb2
     from src.python.grpcio_tests.tests.stress import unary_stream_benchmark_pb2_grpc
-except ImportError:
-    sys.stderr.write("This test must be run from Bazel.\n")
-    sys.exit(1)
 
     _PORT = 5741
     _MESSAGE_SIZE = 4
@@ -102,3 +86,7 @@ def main():
 
     if __name__ == '__main__':
         main()
+
+except ImportError:
+    # NOTE(rbellevi): The test runner should not load this module.
+    pass