Update check_timedatectl from dsa-nagios

Authored by faidon on Fri, Feb 17, 3:52 PM.

Description

Update check_timedatectl from dsa-nagios

Update check_timedatectl to cea5e8b from dsa-nagios. This version among
other things supports timedatectl's new label for NTP on which makes it
compatible with stretch.

Change-Id: I749c2d4b0c95046e2641b2a03a589c0e6b5b41dd