Investigate a persistent python test runner process

[martica]

Similar to the updates made by #783 and #789.

Each test case launches a python process to run it. There was a significant performance improvement from the changes made to the JS test runner by having a persistent process. It may be possible to use the same structure as was used in #789 to launch a single child process and send it code to execute, only terminating it and starting a new one in the case of a test timing out.