EventGroup sometimes times out on start

[nicktindall]

EventGroup#start blocks until the core event loop has started. There have been multiple reports of performStart timing out and throwing an exception. This is unexpected and hasn't been reproduced reliably.

One client reported setting the timeout to 60s and still seeing the timeout, so probably not a case of the timeout being too short.

https://github.com/OpenHFT/Chronicle-Threads/blob/8d15fc227ea9072a921cd439e56dda2f57cff38d/src/main/java/net/openhft/chronicle/threads/EventGroup.java#L394-L412