[WORKER] Name server nodes using node ID.

It is now required for the API server to send the worker each unique
node ID in an UPDATE message, along with the address and port info.
This will be used to name the server in the HAProxy config file. This
step will allow us, in a future update, to be able to report on node
status to statsd, which can then use the node ID to identify failed nodes.

This also includes some unit test updates that does better error
message checking.

Change-Id: Ia7867366200f0d49838c18b7259a06408c4d0a37