Refactor Gracefulshutdown Plugin (#404)

* Refactor gracefulshutdown plugin

 * Remove reporting hanging workers
 * Add ShutdownWithError() func to trigger graceful shutdown
   from outside of the package with error message

* Simplify code

* Increase forcekill timeout to 60 seconds

* Add back reporting of hanging workers

* Upgrade hive.go

* go mod tidy

Co-authored-by: Wolfgang Welz <welzwo@gmail.com>