stop_all_by_force.py didn't work on linux
stop_all_by_force.py: fix v2

This version still sends all the commands to the worker to identify the myria pids
move ax ahead and remove width
stop_all_by_force.py: get rid of need for username length

Apparently username length with `:20` was not cross-platform compatible.
Instead of keeping the user field, making it long, and grepping, let's just
use ps -u <user> to get only processes from the correct user. Easy.
Merge pull request #632 from uwescience/jwang_fixStopAllByForce

stop_all_by_force.py didn't work on linux