monit: widget code cleanup

[Franco Fichtner]

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As witnessed by #7705 the status return from monit API is a bit inconsistent / hard to handle from the consumer side. Maybe this could be simplified to a few defined errors and one good status code (mapped to 0),

[Monviech]

As discussed with @fichtner and @swhite2, changing the widget to only evaluate if the status is either 0 (ok) or =! 0 (not ok) is the best choice. The API does not have to be changed for that, only the widget.