Fix failure in deployment with missing group

The backported prometheus-libvirt-exporter feature missed a safety guard
to avoid failing when deployments haven't updated their environment with
the new group used by that feature.

Deployers will still be warned to add the group when they run the
inventory precheck, but deployments won't be failing if they ignore it.

Change-Id: I1dc5baa8d0da2a454eaa4459e87fc22a275698df
Signed-off-by: Dr. Jens Harbott <[email protected]>
(cherry picked from commit dfdbddf)

Author: osfrickler

ansible/roles/prometheus/tasks/config.yml

@@ -8,7 +8,7 @@
     group: "{{ config_owner_group }}"
     mode: "0770"
   when:
-    - inventory_hostname in groups[item.value.group]
+    - inventory_hostname in groups.get(item.value.group, [])
     - item.value.enabled | bool
   with_dict: "{{ prometheus_services }}"
 
@@ -23,7 +23,7 @@
     dest: "{{ node_config_directory }}/{{ item.key }}/config.json"
     mode: "0660"
   when:
-    - inventory_hostname in groups[item.value.group]
+    - inventory_hostname in groups.get(item.value.group, [])
     - item.value.enabled | bool
   with_dict: "{{ prometheus_services }}"
   notify:
@@ -48,7 +48,7 @@
     dest: "{{ node_config_directory }}/prometheus-server/{{ item.path | basename }}"
     mode: "0660"
   when:
-    - inventory_hostname in groups[service.group]
+    - inventory_hostname in groups.get(item.value.group, [])
     - service.enabled | bool and enable_prometheus_alertmanager | bool
     - prometheus_alert_rules is defined and prometheus_alert_rules.files | length > 0
   with_items: "{{ prometheus_alert_rules.files }}"