fix #1747 mongodb_user support check mode

lib/ansible/modules/extras/database/misc/mongodb_user.py

@@ -183,6 +183,8 @@ def user_add(module, client, db_name, user, password, roles):
 def user_remove(module, client, db_name, user):
     exists = user_find(client, user)
     if exists:
+        if module.check_mode:
+            module.exit_json(changed=True, user=user)
         db = client[db_name]
         db.remove_user(user)
     else:
@@ -222,7 +224,8 @@ def main():
             roles=dict(default=None, type='list'),
             state=dict(default='present', choices=['absent', 'present']),
             update_password=dict(default="always", choices=["always", "on_create"]),
-        )
+        ),
+        supports_check_mode=True
     )
 
     if not pymongo_found:
@@ -274,6 +277,9 @@ def main():
         if update_password != 'always' and user_find(client, user):
             password = None
 
+        if module.check_mode:
+            module.exit_json(changed=True, user=user)
+
         try:
             user_add(module, client, db_name, user, password, roles)
         except OperationFailure, e: