Use a dedicated directory for the mongodb modules (#22187)

* Use a dedicated directory for the mongodb modules
* Missing the RETURN documentation in mongodb_user

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

@@ -189,6 +189,13 @@ EXAMPLES = '''
 
 '''
 
+RETURN = '''
+user:
+    description: The name of the user to add or remove.
+    returned: success
+    type: string
+'''
+
 import os
 import ssl as ssl_lib
 from distutils.version import LooseVersion

test/sanity/pep8/legacy-files.txt

@@ -104,7 +104,7 @@ lib/ansible/modules/cloud/webfaction/webfaction_site.py
 lib/ansible/modules/clustering/consul.py
 lib/ansible/modules/commands/script.py
 lib/ansible/modules/database/influxdb/influxdb_retention_policy.py
-lib/ansible/modules/database/misc/mongodb_user.py
+lib/ansible/modules/database/mongodb/mongodb_user.py
 lib/ansible/modules/database/mssql/mssql_db.py
 lib/ansible/modules/database/mysql/mysql_db.py
 lib/ansible/modules/database/mysql/mysql_replication.py