flux module stats job-ingest doesn't show subprocesses once they are in the trash

[garlick]

Problem: leftover (stuck) validator processes were discovered but flux module stats job-ingest did not show them.

This is as designed. When a worker is no longer needed, its stdin is closed and it is placed in a trash list, freeing the worker slot.

Maybe it would be helpful to add a count of these trashed workers to the pipeline object so that it doesn't look like we have lost track of them.