Get user agent right

BUILD

CMakeLists.txt

Makefile

build.yaml

include/grpc++/grpc++.h

src/cpp/common/channel_arguments.cc

src/cpp/common/version_cc.cc

templates/src/cpp/common/version_cc.cc.template

tools/doxygen/Doxyfile.c++.internal

tools/run_tests/sources_and_headers.json

vsprojects/vcxproj/grpc++/grpc++.vcxproj

vsprojects/vcxproj/grpc++/grpc++.vcxproj.filters

vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj

...s/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj.filters