Use library function to get exitcode from status

[tback]

Shifting by 8 bits will hide the correct exit code in some cases.

On linux sending SIGKILL will produce the log entry.

Worker (pid:22) was sent SIGKILL! Perhaps out of memory

The logline printing the exitcode is not triggered because shifting the status will zero it.

The patched version using os.waitstatus_to_exitcode produces.

Worker (pid:7) exited with code -9
Worker (pid:7) was sent SIGKILL! Perhaps out of memory?

Yes, this is a minute detail. I discovered it when investigating #3330.

[pajod]

Broader refactor (not using that 3.9+ method, but using its os.W* steps) awaiting review over here: #3148

[tback]

thanks, closing in favor of #3148