bindings: python: tests: set the process name

bindings: python: tests: set the process name

When we run the test suite by calling the __main__ function of the module,
the name of the process as visible in the system becomes "python". Let's
set it to "python-gpiod" before running the tests. This way gpiosim will
name its configfs attributes appropriately.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>