core: enable host time drift validation by default

This patch sets the default of host time-drift validation to true.

Change-Id: I70bf171cb10f1dfc3dd864f4244edeb178a0c032
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1145076
Signed-off-by: Eli Mesika <emesika@redhat.com>