Updated openstack/openstack
Project: openstack/heat  3285709c49ec6cda7e9ed1c4b4ee55a14bb159bf

Using six.string_types for python3 compatible

For python3 compatible, using six.string_types instead of
basestring(). six.string_types represent basestring in
python2 and str in python3.

Change-Id: Ib4ba3d164f782601944023b99d6cc1ee2763ee85