code: function Janitor (config) {
    this.config = _.defaults(config || {}, {
      concurrency: 2
    });
  
    if (this.config.clientConfig) {
      this.cwlClient = new AWS.CloudWatchLogs(this.config.clientConfig);
    }
    else {
      this.cwlClient = new AWS.CloudWatchLogs();
    }
  
    // Default maximum.
    this.describeLogGroupsLimit = 50;
  }
docs: -------------------------------------------------------------------------- Class definition. -------------------------------------------------------------------------- 
  @class The main Janitor interface class.
  
  Note that the throttling rate for AWS CloudWatch Log operations is fairly
  low, so it isn't a good plan to increase the concurrency much above 2.
  
  @param {Object} [config]
  @param {Object} [config.clientConfig] Optional AWS client configuration.
  @param {Number} [config.concurrency] Concurrency of AWS deletion operations.