Get metrics for each Spark executor.

def _spark_executor_metrics(self, instance, running_apps, addl_tags, requests_config):
        """
        Get metrics for each Spark executor.
        """
        for app_id, (app_name, tracking_url) in iteritems(running_apps):

            base_url = self._get_request_url(instance, tracking_url)
            response = self._rest_request_to_json(
                base_url, SPARK_APPS_PATH, SPARK_SERVICE_CHECK, requests_config, addl_tags, app_id, 'executors'
            )

            tags = ['app_name:%s' % str(app_name)]
            tags.extend(addl_tags)

            for executor in response:
                if executor.get('id') == 'driver':
                    self._set_metrics_from_json(tags, executor, SPARK_DRIVER_METRICS)
                else:
                    self._set_metrics_from_json(tags, executor, SPARK_EXECUTOR_METRICS)

            if len(response):
                self._set_metric('spark.executor.count', COUNT, len(response), tags)