Update stats from Glances/SNMP server.

def update(self):
        """Update stats from Glances/SNMP server."""
        if self.client_mode == 'glances':
            return self.update_glances()
        elif self.client_mode == 'snmp':
            return self.update_snmp()
        else:
            self.end()
            logger.critical("Unknown server mode: {}".format(self.client_mode))
            sys.exit(2)