smoketest: ntp: re-organize testcases
smoketest: ntp: re-organize testcases

Drop the overcomplex function get_config_value() to search for NTPd
configuration values. Rather assemble the required string and probe for
its presence in the configuration like we do on most other smoketests.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x