Merge pull request #11937 from jtattermusch/kokoro_report_index

tools/internal_ci/helper_scripts/gen_report_index.sh

tools/internal_ci/helper_scripts/prepare_build_linux_rc

tools/internal_ci/helper_scripts/prepare_build_macos_rc

tools/internal_ci/helper_scripts/prepare_build_windows.bat

tools/internal_ci/linux/grpc_basictests_c_cpp_dbg.cfg

tools/internal_ci/linux/grpc_basictests_c_cpp_opt.cfg

tools/internal_ci/linux/grpc_basictests_multilang.cfg

tools/internal_ci/linux/grpc_build_artifacts.cfg

tools/internal_ci/linux/grpc_interop_badserver_java.cfg

tools/internal_ci/linux/grpc_interop_badserver_python.cfg

tools/internal_ci/linux/grpc_interop_matrix.cfg

tools/internal_ci/linux/grpc_interop_tocloud.cfg

tools/internal_ci/linux/grpc_interop_toprod.cfg

tools/internal_ci/linux/grpc_master.cfg

tools/internal_ci/linux/grpc_portability.cfg

tools/internal_ci/linux/grpc_portability_build_only.cfg

tools/internal_ci/linux/grpc_pull_request_sanity.cfg

tools/internal_ci/linux/grpc_sanity.cfg

tools/internal_ci/linux/sanitizer/grpc_c_asan.cfg

tools/internal_ci/linux/sanitizer/grpc_c_msan.cfg