Single source setup for python virtualenv

[buckd]

PR #104 added two new groovy files that require a virtual environment before calling the python code needed. This virtualenv code is duplicated in multiple locations. See if there can be a single groovy call to bat to set up the virtualenv and pass the python command to that virtual environment.

This won't mean we don't need to set up the virtual environment multiple times, just that the code is only located in a single function.