consumer: fix consumeNum to respect the consume timeout

[katreniak]

Steps to reproduce the problem:

• configure consumer with setDefaultConsumeTimeout(1000)
• produce 1 message every 500ms
• call consumer.consume(128, cb)

Actual outcome:

• consume returns batch of 128 messages after 64 seconds

Expected outcome:

• consumer returns batch of ~2 messages after 1 second

KafkaConsumerConsumeNum call underlaying c++ m_consumer->Consume in cycle until

• either the accumulated batch is full
• or the call to c++ m_consumer->Consume times out on the total timeout

KafkaConsumerConsumeNum must enforce its timeout over all m_consumer->Consume invocations altogether.

[katreniak]

Closing in favour of https://github.com/Blizzard/node-rdkafka/pull/1053