some static analyzer improvements for service runner
Summary:
- be more consty (and don't risk detatching containers)
- init members
- don't ql1s to qstring
- use auto when newing an object
Test Plan: test passes
Reviewers: broulik
Reviewed By: broulik
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D28138