Implement a test mode

[ntoll]

A drogulus node may be started in "test mode" for the purposes of, er, testing. This means the following default behaviour will happen:

• Very verbose logging to a specified test.log file.
• Logging also emits to stdout.
• Various non-standard settings may be specified in a configuration file.

The following constraints are enforced on a node running in test mode:

• It will only accept request originating from localhost (on any port).
• It will only be able to send outgoing requests to localhost (on any port).