Fix fluentd upgrade tasks during FFU.

The upgrade task doesn't check for the service existence which make
the upgrade fails during ffu.

We're using the set_facts idiom as it persist between steps.

Closes-Bug: #1757985

Change-Id: I1d3ccd7d3fb641d187f214c20f1d6a4d6113304a

docker/services/fluentd.yaml

@@ -121,9 +121,22 @@ outputs:
             path: /var/cache/containers/fluentd
             state: directory
       upgrade_tasks:
+        - name: Check if fluent.service is deployed
+          command: systemctl is-enabled --quiet fluentd.service
+          ignore_errors: True
+          register: fluentd_enabled_result
+          when:
+            - step|int == 0
+        - name: Set fact fluentd_enabled
+          set_fact:
+            fluentd_enabled: "{{ fluentd_enabled_result.rc == 0 }}"
+          when:
+            - step|int == 0
         - name: Stop and disable fluentd service
-          when: step|int == 2
           service: name=fluentd.service state=stopped enabled=no
+          when:
+            - step|int == 2
+            - fluentd_enabled|bool
       fast_forward_upgrade_tasks:
         - name: Check if fluent.service is deployed
           command: systemctl is-enabled --quiet fluentd.service