Summary:
fix failing tests with Qt 5.11

fix failing tests in random play with Qt 5.11

remove checking for exact index when in random mode because it depends
on Qt behavior that can change

fix failing test: manageaudioplayerTest skipNextTrackWithRandomPlay

Test Plan: tests are all OK with Qt 5.11

Reviewers: astippich, januz

Differential Revision: https://phabricator.kde.org/D15007