Use one shell script for all run_tests_matrix on Kokoro

tools/internal_ci/linux/grpc_master.cfg

tools/internal_ci/linux/grpc_master.sh

tools/internal_ci/linux/grpc_portability.cfg

tools/internal_ci/linux/grpc_portability.sh

tools/internal_ci/linux/grpc_portability_build_only.cfg

tools/internal_ci/linux/grpc_pull_request_sanity.cfg

tools/internal_ci/linux/grpc_run_tests_matrix.sh

tools/internal_ci/linux/grpc_sanity.cfg

tools/internal_ci/linux/grpc_sanity.sh

tools/internal_ci/linux/sanitizer/grpc_c_asan.cfg

tools/internal_ci/linux/sanitizer/grpc_c_asan.sh

tools/internal_ci/linux/sanitizer/grpc_c_msan.cfg

tools/internal_ci/linux/sanitizer/grpc_c_msan.sh

tools/internal_ci/linux/sanitizer/grpc_c_tsan.cfg

tools/internal_ci/linux/sanitizer/grpc_c_tsan.sh

tools/internal_ci/linux/sanitizer/grpc_c_ubsan.cfg

tools/internal_ci/linux/sanitizer/grpc_c_ubsan.sh

tools/internal_ci/linux/sanitizer/grpc_cpp_asan.cfg

tools/internal_ci/linux/sanitizer/grpc_cpp_asan.sh

tools/internal_ci/linux/sanitizer/grpc_cpp_tsan.cfg