isBulk doesn't disable setInterval

[rizowski]

Issue

I've been trying to get node-loggly-bulk running on AWS lambda and have been running into timeout issues. One inconsistency I ran into was passing in the isBulk property and expecting it to not do any sort of polling.

Culprit lines:

https://github.com/loggly/node-loggly-bulk/blob/master/lib/loggly/client.js#L79
https://github.com/loggly/node-loggly-bulk/blob/master/lib/loggly/common.js#L317

Proposed Solutions

I think we could change client.js#L79 to something like this

this.isBulk = options.isBulk || false;

 var defaultBufferOptions = this.isBulk
    ? { size: 500, retriesInMilliSeconds: 30 * 1000 }
    : { size: 1, retriesInMilliSeconds: 100 };

this.bufferOptions = options.bufferOptions || defaultBufferOptions

Another solution I could see, but don't completely know the implications of the change, would be to change common.js#317 to:

if (timerFunctionForBufferedLogs === null && isBulk) {
    timerFunctionForBufferedLogs = setInterval(function() {
      ...   
    }, bufferOptions.retriesInMilliSeconds);
  }