Fix monasca-thresh upgrade

Change Ib225d76076782d695c9387e1c2693bae9a4521d7 introduced a new
upgrade task for monasca-thresh. Because the task is not restricted to
the correct group, it fails while trying to stop monasca_thresh on hosts
not running this container.

Change-Id: I33c2c458a98145315b0de0c069f13b83f59622eb
Closes-Bug: #1952408
(cherry picked from commit b06784e)

Author: priteau

ansible/roles/monasca/tasks/upgrade.yml

@@ -48,6 +48,7 @@
     common_options: "{{ docker_common_options }}"
     name: "{{ monasca_services['monasca-thresh']['container_name'] }}"
   when:
+    - inventory_hostname in groups['monasca-thresh']
     - inventory_hostname != groups['monasca-thresh']|first
 
 - name: Flush handlers