after restarting the service, handle the pid files.

[QingZ11]

After restarting the Nebula Graph server, there is a certain probability of encountering an error message 'process xxx already existed'. The reason is that the previous running process used this ID.

However, it is not practical to manually delete the PID file every time the service is restarted. Is there any way to optimize this?"

ref: https://discuss.nebula-graph.com.cn/t/topic/13036