Disable worker auto-registration by default
This option has security implication if not configured correctly.
The default value WORKER_AUTO_REGISTER_NETMASK allows localhost to register workers, however, if you have a HTTP proxy server LAVA will see the proxy server IP address which might be a localhost. In this case anyone will be able to register a worker and obtain the token.
Work around for #600
Edited by Igor Ponomarev