samba-tool: error handling improvements in delegation.py and samdb.py

[Giampaolo Lauria]

All,

I have put a set of patches on github to improve the way we handle the
samba-tool delegation exceptions.

To view the changes, please follow this URL:
https://github.com/lauria/Samba4/commits/master

Your comments are very much appreciated.

NB You don't need an account on github to view the patches

Thanks,
Giampaolo