[feature-request] Leela_client: "settings.json" Should add "Hostname" parameter for per-node statistics

[Technologov]

For people with dozens of contributing GPU nodes, it becomes hard to see why there's a contributions drop.

Contrib rate drop can be due to multitude of reasons:

1. say T60 (run1) server is down for maintenance, or
2. one or more of node's GPUs are shut-down, (unstable hardware)
3. Leela lc0 engine is simply too old, rejected by server, or
4. leela_client too old...
5. rate of contribution between run1 (T60) and run2 (T50) has been modified by the training server

To add per-node statistics to the website, 1st step is to add it to leela_client:
{"User":"USER","Pass":"PASSWORD","Hostname":$HOSTNAME}
(where currently only User and Pass are passed on to the server.)

Where "$HOSTNAME" is the default, meaning uses system hostname. But the user can modify it to hide the real hostname for privacy reasons, say "Hostname":"Foo".
This way we will have separate statistics per-node, per-user, and also know which nodes belong to which users.
This is the 1st step before improving web-site statistics.

-Technologov, 15.12.2019.

[borg323]

I just made #100 that tries to do the same thing but in a slightly different way: Optionally passes the machine's hostname, gpu name and gpu number to the server, as determined from available information.

[MerickOWA]

#104 is my attempt at this. I actually needed command line control over the localhost setting, so I added that as well as the settings.json possibility.