Set relay state.

def write_switch(self, module_address, state, callback_fn):
        """Set relay state."""
        _LOGGER.info("write_switch: setstate,{},{}{}"
                     .format(module_address, str(state), chr(13)))
        self.subscribe("state," + module_address, callback_fn)
        self.send("setstate,{},{}{}"
                  .format(module_address, str(state), chr(13)))