[PhraseAndIteratorTest] Cleanup, use better variable names

Summary:
Instead of pi1...piN, use something better tractable.

No functional changes.

Reviewers: Baloo, ngraham

Reviewed By: Baloo, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D28500