gbuild: PythonTest: do not invoke the python.bin directly
gbuild: PythonTest: do not invoke the python.bin directly

This works to run the test (with the fixed RPATH in python.bin from
previous commit), but debugging with gdb becomes impossible.

The tests need PYTHONPATH set to find the internal python libraries,
but gdb also uses PYTHONPATH and then tries to load the libraries
there which do not necessarily match the Python version that gdb
is built against.  Invoking the python wrapper shell script avoids this,
and since that "exec"'s python.bin debugging with gdb works too.

Change-Id: I6ea2feb44cebeda1ba2c397baa3837f9f1259a08

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core