shorten launch time by reducing sleep

[rade]

I have discovered that sleeping for 1 second in wait_for_status retries is slowing down weave launch a fair bit. Ideally we'd sleep for a fractional time, but that is non-POSIX so we need to find a way around that.

[dpw]

I think just trying a fractional time and seeing whether sleep dies with an error will be fine. But an alternative would be to do sleep --version and look for an appropriate coreutils version (I doubt POSIX specifies what --version should do, but it is even less likely to cause a problem.)