selftest: Add test for password change when NTLM is disabled

selftest: Add test for password change when NTLM is disabled

When NTLM is disabled, the server should reject NTLM-based password
changes. Changing the password is a bit complicated from python, but
because the server should reject the password change outright with
NTLM_BLOCKED, the test doesn't actually need to provide valid
credentials.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11923
Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Jul 21 13:54:35 CEST 2017 on sn-devel-144