Otherwise htpdate will not "succeed" when the time diff is 0 (i.e.
the clock was already correct) so the success file cannot be used
as an indicator that the system time now is correct, which arguably
is its most important purpose.

This eases post-processing parsing of our logs by external tools by providing
them means to find the last htpdate invocation's log.

When a given certificate cannot be verified, the servers pool
consistency is not considered to be secure enough, and the
client exits without setting time.

This will help supporting multiple servers.