Factoring out lists of url data within KFilePlacesModelTest

Summary:
Instead of reusing the same string lists all over the place
we factor them out, easier to read and maintain.

Depends on D8948

Test Plan: It's within a test

Reviewers: renatoo, ervin, mlaurent

Reviewed By: renatoo, ervin

Subscribers: anthonyfieroni, ervin, ngraham, mlaurent, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D8366