Saves sample metrics from psutil

        :param stats: a dictionary that looks like:
        {
         'memory_info': OrderedDict([('rss', 24395776), ('vms', 144666624)]),
         'io_counters': OrderedDict([('read_count', 4536),
                                    ('write_count', 100),
                                    ('read_bytes', 0),
                                    ('write_bytes', 61440)])
         ...
         }

         This creates a metric like `datadog.agent.collector.{key_1}.{key_2}` where key_1 is a top-level
         key in `stats`, and key_2 is a nested key.
         E.g. datadog.agent.collector.memory_info.rss

def _register_psutil_metrics(self, stats, names_to_metric_types, tags=None):
        """
        Saves sample metrics from psutil

        :param stats: a dictionary that looks like:
        {
         'memory_info': OrderedDict([('rss', 24395776), ('vms', 144666624)]),
         'io_counters': OrderedDict([('read_count', 4536),
                                    ('write_count', 100),
                                    ('read_bytes', 0),
                                    ('write_bytes', 61440)])
         ...
         }

         This creates a metric like `datadog.agent.collector.{key_1}.{key_2}` where key_1 is a top-level
         key in `stats`, and key_2 is a nested key.
         E.g. datadog.agent.collector.memory_info.rss
        """
        if tags is None:
            tags = []
        base_metric = 'datadog.agent.collector.{0}.{1}'
        # TODO: May have to call self.normalize(metric_name) to get a compliant name
        for k, v in stats.iteritems():
            metric_type = names_to_metric_types[k]
            if isinstance(v, dict):
                for _k, _v in v.iteritems():
                    full_metric_name = base_metric.format(k, _k)
                    self._send_single_metric(full_metric_name, _v, metric_type, tags)
            else:
                full_metric_name = 'datadog.agent.collector.{0}'.format(k)
                self._send_single_metric(full_metric_name, v, metric_type, tags)