bpo-37531: Enhance regrtest multiprocess timeout (GH-15345) (GH-15871)

* Write a message when killing a worker process
* Put a timeout on the second popen.communicate() call
  (after killing the process)
* Put a timeout on popen.wait() call
* Catch popen.kill() and popen.wait() exceptions

(cherry picked from commit de2d9eed8bc628533e1628b843cc4c7a5010f6e5)
2 files changed