Convenience to string method.

def device_firmware_str(self, indent):
        """Convenience to string method.
        """
        host_build_ns = self.host_firmware_build_timestamp
        host_build_s = datetime.datetime.utcfromtimestamp(host_build_ns/1000000000) if host_build_ns != None else None
        wifi_build_ns = self.wifi_firmware_build_timestamp
        wifi_build_s = datetime.datetime.utcfromtimestamp(wifi_build_ns/1000000000) if wifi_build_ns != None else None
        s = "Host Firmware Build Timestamp: {} ({} UTC)\n".format(host_build_ns, host_build_s)
        s += indent + "Host Firmware Build Version: {}\n".format(self.host_firmware_version)
        s += indent + "Wifi Firmware Build Timestamp: {} ({} UTC)\n".format(wifi_build_ns, wifi_build_s)
        s += indent + "Wifi Firmware Build Version: {}\n".format(self.wifi_firmware_version)
        return s