Consider changing DisruptorEventQueue.enqueue() to avoid possibility of blocking

[jmullins]

Does it make sense to change DisruptorEventQueue.enqueue() to use RingBuffer.tryNext() instead of RingBuffer.next() to avoid possibly blocking in the case the producers overrun the consumer due to load or a future bug in the consumer?

In all of our use-cases our preference would be to drop the metrics rather than block.

opencensus-java/impl/src/main/java/io/opencensus/impl/internal/DisruptorEventQueue.java

Lines 130 to 142 in aa8ee6a

	DisruptorEnqueuer enqueuer =
	new DisruptorEnqueuer() {
	@Override
	public void enqueue(Entry entry) {
	long sequence = ringBuffer.next();
	try {
	DisruptorEvent event = ringBuffer.get(sequence);
	event.setEntry(entry);
	} finally {
	ringBuffer.publish(sequence);
	}
	}
	};

[saiya]

I created PR for this issue! : #1837