Add mk_apt_hook for automatic cache handling after package installations

Checkmk treasures provide some useful scripts, see:

* i.e. /opt/omd/versions/2.0.0p23.cre/share/doc/check_mk/treasures
* https://github.com/tribe29/checkmk/blob/master/doc/treasures

When mk_apt_hook is installed in /etc/apt/apt.conf.d/ then after every
package installation (included updates) the cache file gets adjusted so
we don't have outdated cache information. This is useful especially when
installing outstanding security updates, then after they get applied
monitoring status corresponds to what's actually present on the system
(instead of dealing with outdated cache files).

Adapted the provided sample and touch
/var/lib/check_mk_agent/cache/*mk_apt.cache only if directory exists.

Thx @mikagrml for the hint with this checkmk treasure.

files/check-mk/mk_apt_hook

@@ -0,0 +1,9 @@
+# HEADER: managed by ansible, do NOT edit manually!
+# retrigger mk-apt
+#
+# If you want use this hook, copy this file to:
+# /etc/apt/apt.conf.d/98mk-apt.
+#
+# For further details please consult the check manual page of apt.
+
+DPkg::Post-Invoke {"test -d /var/lib/check_mk_agent/cache && touch -t 197012181200 /var/lib/check_mk_agent/cache/*mk_apt.cache"; };

tasks/checkmk-plugins.yml

@@ -63,6 +63,14 @@
     group: 'root'
     mode: 0755
 
+- name: Deploy mk_apt_hook for usage with checkmk agent plugin mk_apt
+  copy:
+    src: 'check-mk/mk_apt_hook'
+    dest: '/etc/apt/apt.conf.d/98mk-apt'
+    mode: 0644
+    owner: root
+    group: root
+
 ### checkmk agent plugins
 
 - name: "Deploy checkmk agent plugins"