New health check for cron containers

This tiny script ensures we:
- have a crontab for a specified user
- this crontab isn't empty

If we don't pass a user, it defaults to root.
The emptyness takes into account puppet comments, thus we count
the lines without any leading '#'. By default, puppet adds
some environment variables before the command itself, thus we want
to have at least 2 uncommented lines.

Change-Id: I8ee23f05a2925a20d003dd85b6095fd0b559a23a

healthcheck/cron

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+file="${1:-root}"
+if [ -f /var/spool/cron/${file} ]; then
+  nb_lines=$(grep -cEv '^#' /var/spool/cron/${file})
+  if [ $nb_lines -ge 2 ]; then
+    exit 0
+  fi
+fi
+exit 1

releasenotes/notes/healthcheck-cron-37de4a861e1a1cbf.yaml

@@ -0,0 +1,3 @@
+---
+features:
+  - new health check for "cron" containers, ensuring it exists and has content