[MB-11548] Perform a less strict check on the current time

Perform a less strict check on the current time as we may see
59/61 seconds which isn't neccesarily a clock change.

Also update warning message to show the difference in time.

Change-Id: I524640de83de0159733d2813d55fec523b774e65
Reviewed-on: http://review.couchbase.org/40172
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>