void drainIdleConnectionsOnEventLoop(EventLoop eventLoop) {
        eventLoop.execute(() -> {
            Deque<PooledConnection> connections = connectionsPerEventLoop.get(eventLoop);
            if (connections == null) {
                return;
            }

            for (PooledConnection connection : connections) {
                // any connections in the Deque are idle since they are removed in tryGettingFromConnectionPool()
                connection.setInPool(false);
                LOG.debug("Closing connection {}", connection);
                connection.close();
                connsInPool.decrementAndGet();
            }
        });
    }
Closes idle connections in the connection pool for a given EventLoop. The closing is performed on the EventLoop
thread since the connection pool is not thread safe.

@param eventLoop - the event loop to drain
zuul-core/src/main/java/com/netflix/zuul/netty/connectionpool/PerServerConnectionPool.java