cubicweb-queueing #3227504 async child processes are not wait()ed, zombies ensue [validation pending]

prioritynormal
typebug
done in0.4.0
load0.100
load left0.000
closed by#e1a528685f85 [entities] Wait on child processes to prevent zombies (closes #3227504)
patch[entities] Wait on child processes to prevent zombies (closes #3227504) [applied]