Adjust logging for backup periods that didn't run

[dspruell]

OpenBSD
Perl 5.20.1
rsnapshot 1.3.1

Applicable settings:

verbose         2
retain  hourly  6
retain  daily   7
retain  weekly  4
retain  monthly 3

Currently logging for rsnapshot looks like this:

Jul 26 16:18:38 rsnapshot[2928]: /usr/local/bin/rsnapshot hourly: completed successfully
Jul 26 20:00:03 rsnapshot[14005]: /usr/local/bin/rsnapshot hourly: completed successfully
Jul 26 23:30:01 rsnapshot[11572]: /usr/local/bin/rsnapshot daily: completed successfully
Jul 27 00:00:03 rsnapshot[19342]: /usr/local/bin/rsnapshot hourly: completed successfully

Although the invocation exits successfully, the daily rsnapshot did not actually run because the full retention count of hourly snapshots had not completed yet. I think it would be useful for logging to reflect that more explicitly, perhaps by the log message being modified to indicate that the daily snapshot was skipped.

Jul 26 23:30:01 rsnapshot[11572]: /usr/local/bin/rsnapshot daily: completed successfully but snapshot skipped because /home/snapshots/houly.5 not present (yet)

Also not sure if this is instead a use case better handled by increasingly the verbosity in the config, although I do think it's better that this specific case be made more explicit at the (2) verbosity, rather than requiring more log verbosity overall.