Merge remote-tracking branch 'upstream/master'

src/core/ext/client_config/subchannel_call_holder.c

src/csharp/Grpc.Core.Tests/Internal/AsyncCallTest.cs

src/csharp/Grpc.Core/Internal/AsyncCall.cs

src/csharp/Grpc.Core/Internal/AsyncCallBase.cs

src/csharp/Grpc.IntegrationTesting/InteropClient.cs

test/cpp/interop/client.cc

test/cpp/interop/interop_client.cc

test/cpp/interop/interop_client.h

test/cpp/interop/stress_interop_client.cc

test/cpp/interop/stress_interop_client.h

test/cpp/interop/stress_test.cc

tools/gce/create_linux_performance_worker.sh

tools/gce/linux_performance_worker_init.sh

tools/run_tests/performance/bq_upload_result.py

tools/run_tests/performance/run_netperf.sh

tools/run_tests/run_performance_tests.py