Rename TestService to EchoTestService to prevent name-conflict with

src/proto/grpc/testing/duplicate/echo_duplicate.proto

src/proto/grpc/testing/echo.proto

test/cpp/end2end/async_end2end_test.cc

test/cpp/end2end/client_crash_test.cc

test/cpp/end2end/client_crash_test_server.cc

test/cpp/end2end/end2end_test.cc

test/cpp/end2end/generic_end2end_test.cc

test/cpp/end2end/mock_test.cc

test/cpp/end2end/server_crash_test.cc

test/cpp/end2end/server_crash_test_client.cc

test/cpp/end2end/shutdown_test.cc

test/cpp/end2end/streaming_throughput_test.cc

test/cpp/end2end/thread_stress_test.cc

test/cpp/end2end/zookeeper_test.cc

test/cpp/util/cli_call_test.cc