Issue 50260 - Fix test according to #51222 fix
Description: Managed Entry plugin behaviour was fixed and
returned codes were cleaned up. Now we allow to continue
modrdn and delete managing entry operations execution
even when managed entry doesn't exists.
Also allow 'cn=directory manager' to delete managed entry
on direct update.
Make the updates fail using another way.
https://pagure.io/389-ds-base/issue/50260
https://pagure.io/389-ds-base/issue/51222
Reviewed by: mreynolds (Thanks!)