fix setuptools deprecation

FIX:

#UserWarning: Unknown distribution option: 'tests_require'

Author: mosfet80

example_python/setup.py

@@ -30,7 +30,11 @@
     maintainer_email='[email protected]',
     description='Example usage of generate_parameter_library for a python module',
     license='BSD-3-Clause',
-    tests_require=['pytest'],
+    extras_require={
+        'test': [
+            'pytest',
+        ],
+    },
     entry_points={
         'console_scripts': [
             'test_node = generate_parameter_module_example.minimal_publisher:main'