Backup only when host is reachable; retry backup that was missed due to connection issues

[kees-z]

Similar request here:

Improvements for --run-script-before/after options

from the runscript helptext of --run-script-before-required: If the script returns a non-zero error code or times out, the operation will be aborted. The ParsedResult will always be Failed if the script returns an errorlevel other than 0. There is no way to just skip the backup when a specific condition has met. This can be improved by allowing multiple error levels: Errorlevel 0: Everything is OK, start backup task Errorlevel 1: Everything is OK, but don't run the backup Errorlevel 2: The…