We were previously using the same database (test_treeherder) for both the
jobs and reference data model. I centralized the new db name in the test
settings file. All the test requiring the jobs db or its repository counterpart
can now access it using the `test_project` fixture, while utility functions use
directly the metioned setting. Where the project name is hardcoded in a static
file, I just replaced it with the new name `test_treeherder_jobs`