Logging fixes (logstash-plugins#34)

* Log actual response code

* Log only event data

Author: mpolden

lib/logstash/outputs/http.rb

@@ -120,10 +120,10 @@ def receive(event, async_type=:background)
     request.on_success do |response|
       if response.code < 200 || response.code > 299
         log_failure(
-          "Encountered non-200 HTTP code #{200}",
+          "Encountered non-200 HTTP code #{response.code}",
           :response_code => response.code,
           :url => url,
-          :event => event)
+          :event => event.to_hash)
       end
     end