code: function _createResource() {
      this._log(
          util.format(
              'PromisePool._createResource() - creating client - count=%d min=%d max=%d',
              this._count, this._opts.min, this._opts.max
          ),
          'verbose'
      );
  
      return Promise.resolve(this._opts.create());
  }
docs: Constructs a new resource.
  
  @private
  @this {PromisePool}
  
  @return {Promise.<PromisePool.Client>} A promise for the to-be created client.