Flush out remaining process output at cleanup

[gretac]

At cleanup, processes may not be finished printing when they are killed. This typically happens during debugging to print internal ensemble state. This prevents us from reliably comparing 2 output files, since often some lines will be missing.

[hudon]

We talked a bit about an ensemble "wrapper" that would take care of all process-related responsibilities, such as cleaning up. Thus, the network can order the processes to finish up before terminating.

[hudon]

done in f3ff836