Collect memory stats of LXCs.

def collect(self):
        """
        Collect memory stats of LXCs.
        """
        lxc_metrics = ["memory.usage_in_bytes", "memory.limit_in_bytes"]
        if os.path.isdir(self.config["sys_path"]) is False:
            self.log.debug("sys_path '%s' isn't directory.",
                           self.config["sys_path"])
            return {}

        collected = {}
        for item in os.listdir(self.config["sys_path"]):
            fpath = "%s/%s" % (self.config["sys_path"], item)
            if os.path.isdir(fpath) is False:
                continue

            for lxc_metric in lxc_metrics:
                filename = "%s/%s" % (fpath, lxc_metric)
                metric_name = "%s.%s" % (
                    item.replace(".", "_"),
                    lxc_metric.replace("_in_bytes", ""))
                self.log.debug("Trying to collect from %s", filename)
                collected[metric_name] = self._read_file(filename)

        for key in collected.keys():
            if collected[key] is None:
                continue

            for unit in self.config["byte_unit"]:
                value = diamond.convertor.binary.convert(
                    collected[key],
                    oldUnit="B",
                    newUnit=unit)
                new_key = "%s_in_%ss" % (key, unit)
                self.log.debug("Publishing '%s %s'", new_key, value)
                self.publish(new_key, value, metric_type="GAUGE")