Issue 51222 - It should not be allowed to delete Managed Entry manually
Bug Description: It is possible to delete a managed entry and no error is raised.
Also, while doing delete or modrdn peration on a managing entry and the managed entry
doesn't exist, we should continue the operation.
Fix Description: We should put an entry struct duplicate to SLAPI_ENTRY_PRE_OP pblock
before we execute plugins PRE_OP. Also, we should allow to continue modrdn and delete
managing entry operations execution even when managed entry doesn't exists.
Allow 'cn=directory manager' to delete managed entry on direct update.
Add a test.
Reviewed by: firstyear, tbordaz (Thanks!)