multi: add shutdown logs in subservers

This commit adds a simple shutdown to every subserver to assist
debugging.

contractcourt/chain_arbitrator.go

@@ -893,7 +893,7 @@ func (c *ChainArbitrator) Stop() error {
 		return nil
 	}
 
-	log.Infof("Stopping ChainArbitrator")
+	log.Info("ChainArbitrator shutting down")
 
 	close(c.quit)