[Kicker] Use KRun::runService instead of new KRun

"new KRun" is only meant to run absolute file paths and so breaks when we get a
service with relative entryPath() like when finding a KCModule.

The tempFile argument causes this call to be asynchronous as to not block the UI.
Once we can depend on KDE 5.24 and D1902 is merged, use KRun::runApplication instead

Differential Revision: https://phabricator.kde.org/D1898