Correct usage of sorted() in mongodb_user (ansible#46792)

* Correct usage of sorted() in mongodb_user

sorted() can't be called on a list of dicts
without supplying a key parameter. This is
explained really well in the Sorting HOWTO
https://docs.python.org/3.6/howto/sorting.html#key-functions

This commit fixes ansible#46791

* Fix PEP8 issues

lib/ansible/modules/database/mongodb/mongodb_user.py

@@ -178,6 +178,7 @@
 import ssl as ssl_lib
 import traceback
 from distutils.version import LooseVersion
+from operator import itemgetter
 
 try:
     from pymongo.errors import ConnectionFailure
@@ -319,7 +320,7 @@ def make_sure_roles_are_a_list_of_dict(roles, db_name):
     roles_as_list_of_dict = make_sure_roles_are_a_list_of_dict(roles, db_name)
     uinfo_roles = uinfo.get('roles', [])
 
-    if sorted(roles_as_list_of_dict) == sorted(uinfo_roles):
+    if sorted(roles_as_list_of_dict, key=itemgetter('db')) == sorted(uinfo_roles, key=itemgetter('db')):
         return False
     return True