ntp: Fix service mask when service doesn't exist

The ntp role attempts to mask NTP services that may conflict with
chrony. Currently we are seeing the following failure:

    TASK ntp : Mask alternative NTP clients to prevent conflicts
    Could not find the requested service systemd-timesyncd.service: host

The service_facts module shows that the service is not found:

    "systemd-timesyncd.service": {
        "name": "systemd-timesyncd.service",
        "source": "systemd",
        "state": "stopped",
        "status": "not-found"
    },

According to the Internet, this can happen if there are After/Before
dependencies in one service on another that does not exist.

This change fixes the handling of these not-found services to avoid the
error.

Story: 2009821
Task: 44401

Depends-On: https://review.opendev.org/c/openstack/kayobe/+/827404

Change-Id: I4b8a42704f2b0a145ee9dec433d91df67628cd9d

ansible/roles/ntp/tasks/prepare.yml

@@ -4,7 +4,12 @@
 
 - name: Mask alternative NTP clients to prevent conflicts
   vars:
-    service_exists: "{{ item in ansible_facts.services }}"
+    # NOTE(mgoddard): The service_facts module can return services that are not
+    # present, possibly due to After/Before dependencies in other services.
+    # These show up with a status of 'not-found'.
+    service_exists: >-
+      {{ item in ansible_facts.services and
+         ansible_facts.services[item].status != 'not-found' }}
   systemd:
     name: "{{ item }}"
     enabled: "{{ 'false' if service_exists else omit }}"

releasenotes/notes/story-2009821-b309165e25e77aea.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes an issue with masking NTP services which are not found. See `story
+    2009821 <https://storyboard.openstack.org/#!/story/2009821>`__ for details.