BZ #1128457 - Horizon dashboard -> Not Found

https://bugzilla.redhat.com/show_bug.cgi?id=1128457

Fix 404 on horizon dashboard.

Same fix as posted for packstack (thanks ichavero):
https://bugzilla.redhat.com/show_bug.cgi?id=1129379
https://review.openstack.org/#/c/113592