Raise DuplicatedEnrty error when user exists in delete_container
We do not have right to write to users delete_container. In case that
user already exists in that container and we tried to add entry, we
receive ACIError. This must be checked and DuplicationEntry error must
be raised before.
https://fedorahosted.org/freeipa/ticket/6199
Reviewed-By: Jan Cholasta <jcholast@redhat.com>