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