Add foreman_openstack_satellite_priv_esc.rb

This module exploits a mass assignment vulnerability in the 'create'
action of 'users' controller of Foreman and Red Hat OpenStack/Satellite
(Foreman 1.2.0-RC1 and earlier) by creating an arbitrary administrator
account.
Land #2143, @rcvalle's module for CVE-2013-2113
Final cleanup for foreman_openstack_satellite_priv_esc