[dnsdist] Marking downstream Unexplained

[Aleš Rygl]

> > I've just added a lot of log messages to be able to debug health check
> > failures, they are only enabled in verbose mode _and_ if
> > setVerboseHealthChecks(true) is used.
> 
> How nice!
> 

I have just realized that in verbose mode all queries are logged (I was not 
aware of that). I am affraid that running dnsdist in verbose mode is not a 
good idea in production because of the ammount of logs and... without verbose 
mode setVerboseHealthChecks(true) does not have the effect... what now?

Ales