In, Chapter 1. Introduction In order to successfully enable/disable repositories I had to first run $ yum clean all before I proceeded with $ sudo yum-config-manager --disable rhel-server-ost-6-preview-rpms I guess something needed to update that the openstack product had been consumed by subscription manager. If yum-config-manager didn't output details of the yum repository settings you know it did nothing.
*** This bug has been marked as a duplicate of bug 889306 ***