smbd: add smbd_impersonate_debug_create() helper

smbd: add smbd_impersonate_debug_create() helper

This will be used to implement no-op impersonation
for the create_conn_struct_as_root() case were we
don't really have other unrelated events in the loop
and only need a valid tevent wrapper context to avoid
double free on the raw event context on teardown.

This also adds useful debugging instead of being
a full no-op wrapper.

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