Many tests still invoke the logic to automatically assign a port number to the main tub

[exarkun]

The default behavior for starting a client without [node]tub.port configured is to try to automatically allocate a tcp port.

This logic is failure prone because it's not actually possible to reliably allocate a tcp port that will be unused at some future point.

Many tests still trigger this behavior by creating nodes without this configuration item. As a result, test suite runs often include a spurious failure.

[GitHub <noreply@…>]

In 07ffde3/trunk:

Merge pull request #1158 from tahoe-lafs/3838.more-main-tub-cleanup

More "main tub" initialization cleanup in test code

Fixes: ticket:3838