Add sanity test to check for unwanted files.

docs/docsite/rst/dev_guide/testing/sanity/no-unwanted-files.rst

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+Sanity Tests » no-unwanted-files
+================================
+
+Specific file types are allowed in certain directories:
+
+- ``lib`` - All content must reside in the ``lib/ansible`` directory.
+
+- ``lib/ansible`` - Only source code with one of the following extensions is allowed:
+
+  - ``*.cs`` - C#
+  - ``*.ps1`` - PowerShell
+  - ``*.psm1`` - PowerShell
+  - ``*.py`` - Python

test/sanity/code-smell/no-unwanted-files.json

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+{
+    "prefixes": [
+        "lib/"
+    ],
+    "output": "path-message"
+}

test/sanity/code-smell/no-unwanted-files.py

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+#!/usr/bin/env python
+"""Prevent unwanted files from being added to the source tree."""
+import os
+import sys
+
+
+def main():
+    """Main entry point."""
+    paths = sys.argv[1:] or sys.stdin.read().splitlines()
+
+    allowed_extensions = (
+        '.cs',
+        '.ps1',
+        '.psm1',
+        '.py',
+    )
+
+    skip = (
+        # allowed special cases
+        'lib/ansible/config/base.yml',
+        'lib/ansible/config/module_defaults.yml',
+        # temporary skip, relocate these to docs
+        'lib/ansible/modules/cloud/amazon/GUIDELINES.md',
+        'lib/ansible/modules/cloud/openstack/README.md',
+        'lib/ansible/modules/cloud/ovirt/README.rst',
+    )
+
+    skip_directories = (
+        'lib/ansible.egg-info/',
+        'lib/ansible/galaxy/data/',
+    )
+
+    for path in paths:
+        if path in skip:
+            continue
+
+        if any(path.startswith(skip_directory) for skip_directory in skip_directories):
+            continue
+
+        if path.startswith('lib/') and not path.startswith('lib/ansible/'):
+            print('%s: all "lib" content must reside in the "lib/ansible" directory' % path)
+            continue
+
+        ext = os.path.splitext(path)[1]
+
+        if ext not in allowed_extensions:
+            print('%s: extension must be one of: %s' % (path, ', '.join(allowed_extensions)))
+
+
+if __name__ == '__main__':
+    main()