copy service account key logic

tools/jenkins/build_interop_image.sh

tools/jenkins/grpc_interop_csharp/build_interop.sh

tools/jenkins/grpc_interop_cxx/build_interop.sh

tools/jenkins/grpc_interop_go/build_interop.sh

tools/jenkins/grpc_interop_java/build_interop.sh

tools/jenkins/grpc_interop_node/build_interop.sh

tools/jenkins/grpc_interop_php/build_interop.sh

tools/jenkins/grpc_interop_ruby/build_interop.sh