Fix bug #5568 net rpc trustdom add broken !

Fix bug #5568 net rpc trustdom add broken !
net rpc trustdom add was broken. The default 10second timeout can be too short
to create an account on a Samba DC (calling out to a script), error message
reporting was poor, and more importantly the new marshalling code for
user_info23 was broken (maps onto a user_info21 but doesn't clear the
user_info23 struct before marshalling, leaving an uninitialized size field -
give "alloc failure").
Jeremy.
(cherry picked from commit 52552623277726c2f28a992f68d8bc22982bab28)