Improve emitter logic: Only run upgrade tasks if full run not needed.

If a machine's timestamp is older than the date of the last
git commit, do a full ansible run.  If the time stamp is older
than the trigger time (given as argument to 'emitter') but
younger than the latest git commit, run only the upgrade tasks.

A single outdated machine triggers the full run for all
machines in the list.

lmn-client.yml

@@ -74,7 +74,8 @@
 
   roles:
     - lmn_network
-    - up2date_debian
+    - role: up2date_debian
+      tags: upgrade
     - lmn_sssd
     - lmn_mount
     - lmn_kde
@@ -85,9 +86,10 @@
     - lmn_security
 
   tasks:
-    - name: Timestamp successfull ansible run
+    - name: Timestamp successfull run
       ansible.builtin.shell: date --iso-8601=seconds >> /root/.ansible/stamps
       changed_when: False
+      tags: upgrade
 
 ## Temporary fixes and quirks:
     - name: Fix 8086:4909 external graphics card