Update use of PythonRunScriptService as used by Python PyDev Workflow Actor

Previously we used magic global input variables (script_inputs in PyDev
actor or just the variable names in Python actor), now the script defines
a method that can be called (by default "run").

See python_script5.py (As used by python_pydev_numpy_example1.moml)
Limit Python version to < 3.0

On machines where Python 2 and Python 3 is installed, the code picks
up Python 3. This was unintended and it was trying to find the most
recent version of Python 2 instead.