utils: fix process races when killing processes (#5721)
utils: fix process races when killing processes (#5721)

airflow.utils.helpers.reap_process_group() can throw uncaught OSErrors
if processes exit at the wrong time in its execution. Fix this by
catching all OSErrors that can arise due to a process race, and
returning from them when the error is ESRCH (process not found).

(cherry picked from commit 18d32d969e8e706fbdf16eb6d60406c4dc223c1e)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow