onevent/startupshutdown: run command once per server block (#1934)

onevent/on.go

@@ -20,9 +20,12 @@ func setup(c *caddy.Controller) error {
 	}
 
 	// Register Event Hooks.
+	c.OncePerServerBlock(func() error {
 		for _, cfg := range config {
 			caddy.RegisterEventHook("on-"+cfg.ID, cfg.Hook)
 		}
+		return nil
+	})
 
 	return nil
 }

startupshutdown/startupshutdown.go

@@ -36,9 +36,12 @@ func Startup(c *caddy.Controller) error {
 	}
 
 	// Register Event Hooks.
+	c.OncePerServerBlock(func() error {
 		for _, cfg := range config {
 			caddy.RegisterEventHook("on-"+cfg.ID, cfg.Hook)
 		}
+		return nil
+	})
 
 	fmt.Println("NOTICE: Startup directive will be removed in a later version. Please migrate to 'on startup'")