python/ntacls: we only need security.SEC_STD_READ_CONTROL in order to get the ACL

python/ntacls: we only need security.SEC_STD_READ_CONTROL in order to get the ACL

We should avoid security.SEC_FLAG_MAXIMUM_ALLOWED otherwise
we may get NT_STATUS_SHARING_VIOLATION when we run
'samba-tool domain backup online' against a Windows DC.
Windows DCs have hidden folders for the NtFrs or Dfsr services,
which are locked by the running service.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13917

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>