Description of problem:

When a user is deleted in a LDAP or AD backend it happens that some leftover information remains in the assignments table. When it happens we can see in the project the user uuid but we are not able to delete it.

We would like to have a tool to manipulate the assignments directly without having to go to the database in order to achieve this task, for example

# keystone assignment-delete <tenant> <user>

or a way to resync the current assignment with the backend and remove from the database the deleted users

Version-Release number of selected component (if applicable):
OSP 6

How reproducible:
always

Steps to Reproduce:
 
Starting from a keystone using AD backend:

1. Give a role in a project to the user
2. Delete the user from the backend
3.

Actual results:
A uuid is displayed in the project users
It is not possible to delete it manually


Expected results:
- uuid not displayed in the project users
- a way to delete the assignement when it happens



Additional info: