Some extensions when we delete system users.

Before we delete a user account - we kill it's session and force a log-out. In theory the user could log back in in a very tiny window and prevent the deletion of the account.
To prevent this loophole the account should be disabled before we force a logout.

Source code: https://github.com/vyos/vyos-1x/blob/175b0a082808955adba811f18424a126e798dd32/src/conf_mode/system-login.py#L253-L259

In addition we only try to delete the user account once - if this fails - the account persists. userdel(8) should be called in a loop which only exists once the account deletion was completed successfully.