fix mysql_info crash if PUBLIC role is used on MariaDB 10.11+ (#712)

* tests: grant a privilege to the PUBLIC role to force the module to fail

* skip the PUBLIC role from the users migration example

* Cut the 3rd matching group as it fails to match roles without quotes

The group purpose was to match the closing quotes. We don't need the
value after the TO. So we can ignore this entirely.

* add MariaDB role detection

* Add changelog fragment

* doc: add notes that users_info doesn't support MariaDB roles.

plugins/module_utils/user.py

@@ -662,7 +662,7 @@ def privileges_get(cursor, user, host, maria_role=False):
         if not maria_role:
             res = re.match("""GRANT (.+) ON (.+) TO (['`"]).*\\3@(['`"]).*\\4( IDENTIFIED BY PASSWORD (['`"]).+\\6)? ?(.*)""", grant[0])
         else:
-            res = re.match("""GRANT (.+) ON (.+) TO (['`"]).*\\3""", grant[0])
+            res = re.match("""GRANT (.+) ON (.+) TO .*""", grant[0])
 
         if res is None:
             # If a user has roles assigned, we'll have one of priv tuples looking like