def command(self, server_id, command, *args):
        """run command
        Args:
            server_id - server identity
            command - command which apply to server
        """
        server = self._storage[server_id]
        try:
            if args:
                result = getattr(server, command)(*args)
            else:
                result = getattr(server, command)()
        except AttributeError:
            raise ValueError("Cannot issue the command %r to server %s"
                             % (command, server_id))
        self._storage[server_id] = server
        return result
run command
        Args:
            server_id - server identity
            command - command which apply to server