start_sockproc: line 55: kill: (47) - No such process

When I restart my container, there are still /tmp/ files lying around ( `auto-ssl-sockproc.pid shell.sock` ) and resty-auto-ssl throws this error:
```
start_sockproc: line 55: kill: (47) - No such process
```

I'm guessing that if exit code is 47 in start_sockproc then it should swallow the error.

Start at the start_sockproc entry point and inspect line 55, then reproduce a container restart with auto-ssl-sockproc.pid and shell.sock left in /tmp. Check how the process cleanup handles a missing PID, and consider the issue resolved when restart no longer emits the kill error while stale files are handled safely.

Written by the indexing model from the issue text.