Add Icinga plug-in & NRPE check for EventLogging jobs

This patch adds a shell script that acts as an Icinga plug-in for EventLogging.
It walks the job instance definition tree (/etc/eventlogging.d) and checks that
each defined instance is running. If /etc/eventlogging.d is missing, it exits
with status UNKNOWN. If one or more defined instances are stopped, it emits a
CRITICAL status with a message that enumerates the stopped services. If all
defined instances are running, it exits with status OK.

Change-Id: I88af621c470f1cc7cc557bcdbbc2dee5806d7c01
Merge "Add Icinga plug-in & NRPE check for EventLogging jobs" into production