r743: Start on a NETLOGON server in Samba4.

r743: Start on a NETLOGON server in Samba4.

Currently this only authentiates the machine, not real users.

As a consequence of running the Samba4 NETLOGON test against Samba4, I
found a number of issues in the SAMR server, which I have addressed.
There are more templates in the provison.ldif for this reason.

I also added some debug to our credentials code, and fixed some bugs
in the auth_sam module.

The static buffer in generate_random_string() bit me badly, so I
removed it in favor of a talloc based system.

Andrew Bartlett