net: fix post join verification.

net: fix post join verification.

This patch is based on commit 30d99d8ac3379caadc5bdb353977149d1ee16403
and just a little modified to apply on 3-0-test.

Guenther

Original commit message:

r24789: Add implementation of machine-authenticated connection to netlogon
pipe used when connecting to win2k and newer domain controllers. The
server may be configured to deny anonymous netlogon connections which
would stop domain join verification step. Still, winnt domains require
such smb sessions not to be authenticated using machine credentials.
Creds employed in smb session cannot have a username in upn form, so
provide the separate function to use machine account.

rafal