Set py_modules to 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.

Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Change-Id: Id0b18670847a78c55295c74a7070b580d90ffed0

setup.py

@@ -5,5 +5,6 @@
 import setuptools
 
 setuptools.setup(
-    setup_requires=['pbr'],
+    setup_requires=['pbr>=2.0.0'],
+    py_modules=[],
     pbr=True)