Add a device to the list which doesn't have serial number

[mhiramat]

lium dut list --add requires serial number to add a device to the local DUT list. But some devices don't have the serial number.
Use some hash (e.g. from IPv6 addr) number if the device has no serial number. (But warn user that this device name is local one)

[mhiramat]

Simply using the random serial number does not work. We should use MAC addr.