Improve the stability of instance creation on a multithreaded environment

https://github.com/frugalos/liberasurecode/blob/ed4582200b9906ff9a14a4ee6a95d9b312e5241e/src/lib.rs#L175

`std::thread::sleep(Duration::from_millis(10))` is not enough and causes build failures on TravisCI. We need a new solution.

See #2 .