Added doc for galaxy-metadata sanity test and fixed the errors.

docs/docsite/rst/dev_guide/testing/sanity/galaxy-metadata.rst

@@ -0,0 +1,5 @@
+galaxy-metadata
+===============
+
+* Validates the required keys (namespace, name, version, readme, authors) for the collection galaxy.yml metadata file.
+* If the required keys aren’t present or if the required and other keys contain ``null`` value in the galaxy.yml file then this sanity test will throw an error.

test/lib/ansible_test/_data/sanity/code-smell/galaxy-metadata.py

@@ -1,8 +1,9 @@
 #!/usr/bin/env python
-"""Schema validation of ansible-core's ansible_builtin_runtime.yml and collection's meta/runtime.yml"""
+"""Validates the required keys (namespace, name, version, readme, authors) for the collection galaxy.yml metadata file"""
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
+import re
 import sys
 import yaml
 
@@ -12,6 +13,7 @@ from voluptuous.humanize import humanize_error
 
 from ansible.module_utils.six import string_types
 
+
 def validate_galaxy_metadata_file(path):
     """Validate explicit galaxy.yml metadata file"""
     try:
@@ -64,5 +66,6 @@ def main():
         if path == collection_galaxy_file:
             validate_galaxy_metadata_file(path)
 
+
 if __name__ == '__main__':
     main()