Add a factory method for BuildTestBase's copyCodebase() Finder object.

Problem/Motivation

In build tests, you can provide an iterator for copyCodebase().

If none is provided, BuildTestBase uses a symfony Finder object to generate an iterator. It creates the finder object internally, so you can't just add extra filters on the finder, you have to create a whole different one.

This makes it difficult to remain consistent in what copyCodebase() will copy, because everyone has to re-invent this particular wheel.

Proposed resolution

Add a factory method to BuildTestBase which makes the finder object. This allows test authors to use the same finder constraints that copyCodebase() would, but also add their own.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet