selftest: Pass the dcerpc binding object to self.waitForMessages in auth_log

selftest: Pass the dcerpc binding object to self.waitForMessages in auth_log

This ensures that object is not cleaned up, triggering a disconnect before we get back
the audit messages.  Otherwise they can be lost when the server task calls exit()
while the message thread is still trying to send them.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>