engine: fix high memory usage in FluentLogEventRouter

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

lib/fluent/engine.rb

@@ -153,13 +153,13 @@ def now
 
     def run
       begin
+        @fluent_log_event_router.start
+
         $log.info "starting fluentd worker", pid: Process.pid, ppid: Process.ppid, worker: worker_id
         @root_agent_mutex.synchronize do
           start
         end
 
-        @fluent_log_event_router.start
-
         $log.info "fluentd worker is now running", worker: worker_id
         sleep MAINLOOP_SLEEP_INTERVAL until @engine_stopped
         $log.info "fluentd worker is now stopping", worker: worker_id