Circuit breaker panel memory leak (?)

[ignasi35]

While reviewing proposal to port CircuitBreakersPanel from Lagom to akka/akka I think I saw a memory leak.

Circuit breakers may be added to the panel's breakers ConcurrentHashMap but are never removed.

It is rare for Lagom users to access the CircuitBreakersPanel and there'll probably only be as many instances as downstream lagom services. But the CircuitBreakersPanel may be used to arbitrarily create instances thus leaking.