tests py_credentials: Fix encrypt_netr_crypt_password test

tests py_credentials: Fix encrypt_netr_crypt_password test

The test uses NetrServerPasswordSet2 to change a password, this tests
the end to end encryption.  The original call to NetrServerPasswordSet2
was not utf-16 encoding the new password.  However the call to
netr_DsrEnumerateDomainTrusts was using cached credentials and not
using the new password, so this was not detected.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Garming Sam <garming@samba.org>
Autobuild-Date(master): Thu Jun 29 06:50:32 CEST 2017 on sn-devel-144