'NTPD on nodes was not synchronized' on reverting an env snapshot where openstack config was reconfigured

[Dmitriy Kruglov]

Detailed bug description:
Some service reconfiguration system tests fail with 'NTPD on nodes was not synchronized: [(u'slave-02', []), (u'slave-03', []), (u'slave-04', [])]' kind of error when reverting a snapshot where config(s) were already reconfigured (as per logic of the previous test).
https://product-ci.infra.mirantis.net/job/10.0.system_test.ubuntu.services_reconfiguration_thread_1/76/testReport/(root)/reconfigure_nova_ephemeral_disk/reconfigure_nova_ephemeral_disk/
https://product-ci.infra.mirantis.net/job/10.0.system_test.ubuntu.services_reconfiguration_thread_1/76/testReport/(root)/preservation_config_after_reset_and_preconfigured_deploy/preservation_config_after_reset_and_preconfigured_deploy/

The affected tests:
reconfigure_nova_ephemeral_disk
apply_config_for_node_with_multiple_role
multiple_apply_config
reconfiguration_scalability
preservation_config_after_reset_and_preconfigured_deploy

Steps to reproduce:
Please refer to the referenced auto system tests for additional details.

Description of the environment:
MOS 10.0-mitaka, ISO build #27.