def _retry_until_powered_on(self, power):
        """This method retries power on operation.

        :param: power : target power state
        """
        # If the system is in the same power state as
        # requested by the user, it gives the error
        # InvalidOperationForSystemState. To avoid this error
        # the power state is checked before power on
        # operation is performed.
        status = self.get_host_power_status()
        if (status != power):
            self._perform_power_op(POWER_STATE[power])
            return self.get_host_power_status()
        else:
            return status
This method retries power on operation.

        :param: power : target power state