Use positive word for method name

Negative word may confuse with us.

lib/droonga/serf/agent.rb

@@ -138,7 +138,7 @@ def on_standard_output(line_buffer, data)
               hour, minute, second = $4, $5, $6
               level = $7
               content = $POSTMATCH
-              return if suppressed_log_message?(content)
+              return unless needed_log_message?(content)
               level = normalize_level(level)
               logger.send(level, content)
             else
@@ -150,16 +150,16 @@ def on_standard_output(line_buffer, data)
         end
       end
 
-      def suppressed_log_message?(content)
+      def needed_log_message?(content)
         case content
         when /\Amemberlist: Failed to receive remote state: EOF\z/
           # See also: https://github.com/hashicorp/consul/issues/598#issuecomment-71576948
-          true
+          false
         when /\Aagent: Script .*droonga-engine-serf-event-handler.* slow, execution exceeding/
           # Droonga's serf event handler can be slow for absorbing or some operations.
-          true
-        else
           false
+        else
+          true
         end
       end