Set py_modules to an empty list in setup.py

This prevents setuptools 61.0.0 doing autodiscovery and failing
as this is an ansible role, not a python module.

Change-Id: I93f392fec7088a2c99d36fdf4292fec775bc01fe

setup.py

@@ -17,4 +17,5 @@ import setuptools
 
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
+    py_modules=[],
     pbr=True)