Disable auto-discovery for setuptools

Since setuptools release (61.0.0) ansible-role-lunasa-hsm's
package build command (python3 setup.py sdist bdist_wheel) is
finding 'defaults' directory as a python module and including
it in the built package. That's not correct as defaults is just
providing data files properly managed as data_files and there is no
actual python module, setup.py is just used as build/install tooling.

Change-Id: I759d63ede6b9d5ebedf3ccc7dcb808055a0d009a

setup.py

@@ -16,4 +16,5 @@ import setuptools
 
 setuptools.setup(
     setup_requires=['pbr'],
-    pbr=True)
+    pbr=True,
+    py_modules=[])