Fixes T5665: kolabd should now terminate its child processes on exit
Summary: This patch ensures that kolabd will terminate his forked childs
Test Plan: Tested on Debian 9 and Debian 10
Reviewers: PyKolab Developers, vanmeeuwen
Reviewed By: PyKolab Developers, vanmeeuwen
Differential Revision: https://git.kolab.org/D853