Skip resmo.ntp role if ntp_service_enabled is false

We enable ntpd by default, and provide a variable to disable it -
ntp_service_enabled. It is also automatically disabled if the user
enables the chrony container (kolla_enable_chrony).

However, setting ntp_service_enabled to false will cause the host
configure commands to fail due to a bug in the resmo.ntp role. This is
because it tries to configure the ntpd service in systemd, but it will
not exist so the task fails.

This change fixes the issue by skipping the resmo.ntp role if the NTP
service is disabled.

Change-Id: I640873c11ceae5008030dc03984c089a410a0cee
Story: 2007384
Task: 38968

ansible/ntp.yml

@@ -8,3 +8,8 @@
       become: True
     - role: resmo.ntp
       become: True
+      # NOTE(mgoddard): The resmo.ntp role fails if ntp_service_enabled is set
+      # to false, since it tries to disable the ntpd service which does not
+      # exist. Skip the role if it is disabled.
+      # https://storyboard.openstack.org/#!/story/2007384.
+      when: ntp_service_enabled | bool

releasenotes/notes/skip-ntp-if-disabled-585c756f01b34bfa.yaml

+---
+fixes:
+  - |
+    Fixes an issue where host configuration would fail if
+    ``ntp_service_enabled`` is set to ``false`` or ``kolla_enable_chrony`` is
+    set to ``true``. See `story 2007384
+    <https://storyboard.openstack.org/#!/story/2007384>`__ for details.