Add a function to parse out Python test files
Add a function to parse out Python test files

This allows CMake to discover the tests available at configure time.
This is required anyways since adding a test already required rerunning
the configure step to rewrite the CTest file for the new test.

mathstuf/sprokit,linus-sherrill/sprokit,Kitware/sprokit,linus-sherrill/sprokit,Kitware/sprokit,mathstuf/sprokit,Kitware/sprokit,linus-sherrill/sprokit,mathstuf/sprokit,mathstuf/sprokit,linus-sherrill/sprokit,Kitware/sprokit