s4/dsdb/tests/python: PY3 port samba4.sam.python test

s4/dsdb/tests/python: PY3 port samba4.sam.python test

Misc changes to ensure samba4.sam.python test will run under
python2/python3

* various objectSID values when formatted need to be treated
as strings for tests.

* DOMAIN_RID_USERS, DOMAIN_RID_DOMAIN_MEMBERS, DOMAIN_RID_DCS,
  DOMAIN_RID_READONLY_DCS are all integers (but attibutes are
  ldb.bytes in PY3, need to adust various assertEquals.
* Make sure password is encoded correctly

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>