Horizon needs this selinux boolean set

See:
https://bugzilla.redhat.com/show_bug.cgi?id=978568
https://github.com/stackforge/packstack/blob/master/packstack/puppet/templates/horizon.pp

Change-Id: I1cbf181625bfcb3b23fd57d8342fb72743342ebc
Merge "Horizon needs this selinux boolean set"