close multiprocess executor event queue in parent process rather than child process
Summary: Some sporadic failures during multiprocess execution tests point to an issue with the queue still writing events after it has been closed. Try closing the queue in the process that created it (which is probably better anyways?) and wait to close it until after the child process has been joined.
Test Plan: BK + Azure (no more BrokenPipeError in windows test output)
Reviewers: alangenfeld, schrockn, max
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D5152