Ensure that any stray kscreenlocker_greet processes are cleaned up at the end...

Ensure that any stray kscreenlocker_greet processes are cleaned up at the end of CI runs (Jenkins side now).
This should ensure that hung processes that consume an entire CPU core are not left behind - and reduce the overall performance of that CI worker server until it is cleaned up.

CCMAIL: plasma-devel@kde.org
CCMAIL: kwin@kde.org