Improve model string generation to be more unique

The model is not unique on two machines with the same operating system and version.
For example, you could replace platform.platform() with ...

import uuid
mac_int = uuid.getnode( ) # get mac address
mac_hex = format( mac_int, 'x') # convert mac to hex
model_uuid = uuid.uuid3( uuid.NAMESPACE_OID, mac_hex) # generate md5 hash
model = model_uuid.hex # convert uuid to hex string