Quiet the logstash handler loading message

@s0undt3ch FYI.  If you think this is a bad change, I'd be happy to
discuss it with you, but 99% of salt users don't use that handler (as
far as I know) and it's just garbage in the debug log.
Merge pull request #9361 from basepi/logstashquiet

Quiet the logstash handler loading message