Get the device state (i.e. ON or OFF).

def state(self):
        """Get the device state (i.e. ON or OFF)."""
        response =  self.SOAPAction('GetSocketSettings', 'OPStatus', self.moduleParameters("1"))
        if response is None:
            return 'unknown'
        elif response.lower() == 'true':
            return ON
        elif response.lower() == 'false':
            return OFF
        else:
            _LOGGER.warning("Unknown state %s returned" % str(response.lower()))
            return 'unknown'