interop: increase xds test client rpc timeout (#3579)
interop: increase xds test client rpc timeout (#3579)


stanley-cheung/grpc-go,menghanl/grpc-go,grpc/grpc-go,menghanl/grpc-go,grpc/grpc-go,stanley-cheung/grpc-go,dfawley/grpc-go,dfawley/grpc-go