Enable the new Python Torperf to start and stop tor processes
After #3280 (closed) is done, the new Torperf should also be able to start and stop its tor processes. Starting the processes should happen automatically after reading the configuration file. Further, the new Torperf should have a config option or switch to stop all running tor processes. Torperf could look at the tor.pid files in the directories under
DataDirectory and sending these processes a kill signal.
Assigning to tomb upon request.