Debian: CVE-2018-6536: icinga2 -- security update

An issue was discovered in Icinga 2.x through 2.8.1. The daemon creates an icinga2.pid file after dropping privileges to a non-root account, which might allow local users to kill arbitrary processes by leveraging access to this non-root account for icinga2.pid modification before a root script executes a "kill `cat /pathname/icinga2.pid`" command, as demonstrated by icinga2.init.d.cmake.