Return if target device is discovered.

def is_discovered(self):
        """Return if target device is discovered."""
        if self.target_device is None:
            return False

        if None in (self.target_device.version_text, self.target_device.os_type, self.target_device.os_version,
                    self.target_device.inventory_text, self.target_device.family, self.target_device.platform):
            return False
        return True