[Reviewer: Jim] Initialize the cond var to use CLOCK_MONOTONIC

Jim,

Please can you review my fix to initialize the cond var to use CLOCK_MONOTONIC - as it is, pop() calls always return immediately (because CLOCK_MONOTONIC times are always less than CLOCK_REALTIME).  Without this, on failure, we tight-loop if the SAS is unavailable.

This has already been reviewed by Ellie, but I believe you own this repo so wanted to give you an opportunity to object.  I've live-tested but not UT-ed (as I don't think there is currently any infrastructure for this).

Thanks,

Matt