pyglue: test cases for Python API

Added infrastructure to run exciting test cases on PyOpenColorIO.

It would be nice to extend this so it can doctest the Sphinx docs, to verify the examples work, although I've not looked into this much

> To run:
>
>     $ mkdir build && cd build
>     $ cmake -D OCIO_BUILD_TESTS=yes ..
>     $ make
>     $ make test
>     $ cat Testing/Temporary/*.log
>
> Or you can execute "build/src/pyglue_tests/ocio_pyglue_tests.sh"