Fix doc reference in settings.rst: 'hz' should be 'horizon'
Fix doc reference in settings.rst: 'hz' should be 'horizon'

It's been renamed to 'horizon' (https://review.openstack.org/#/c/206760/)

Change-Id: I1edba2e089c341758b2ab48c4fdebe498a77981d

yeming233/horizon,Mirantis/mos-horizon,openstack/horizon,maestro-hybrid-cloud/horizon,Tesora/tesora-horizon,vladryk/horizon,Mirantis/mos-horizon,damien-dg/horizon,NeCTAR-RC/horizon,maestro-hybrid-cloud/horizon,django-leonardo/horizon,Tesora/tesora-horizon,redhat-cip/horizon,dan1/horizon-x509,idjaw/horizon,gerrive/horizon,BiznetGIO/horizon,saydulk/horizon,davidcusatis/horizon,tqtran7/horizon,Tesora/tesora-horizon,takeshineshiro/horizon,Tesora/tesora-horizon,wolverineav/horizon,redhat-cip/horizon,damien-dg/horizon,django-leonardo/horizon,dan1/horizon-x509,BiznetGIO/horizon,redhat-openstack/horizon,bigswitch/horizon,Mirantis/mos-horizon,bac/horizon,coreycb/horizon,vladryk/horizon,ChameleonCloud/horizon,damien-dg/horizon,idjaw/horizon,wolverineav/horizon,BiznetGIO/horizon,tqtran7/horizon,redhat-cip/horizon,FNST-OpenStack/horizon,django-leonardo/horizon,NeCTAR-RC/horizon,bigswitch/horizon,takeshineshiro/horizon,coreycb/horizon,takeshineshiro/horizon,sandvine/horizon,noironetworks/horizon,dan1/horizon-x509,endorphinl/horizon-fork,coreycb/horizon,maestro-hybrid-cloud/horizon,bac/horizon,FNST-OpenStack/horizon,damien-dg/horizon,philoniare/horizon,redhat-openstack/horizon,sandvine/horizon,wolverineav/horizon,anthonydillon/horizon,maestro-hybrid-cloud/horizon,redhat-openstack/horizon,saydulk/horizon,openstack/horizon,philoniare/horizon,NeCTAR-RC/horizon,endorphinl/horizon-fork,noironetworks/horizon,sandvine/horizon,davidcusatis/horizon,Dark-Hacker/horizon,philoniare/horizon,ChameleonCloud/horizon,tqtran7/horizon,idjaw/horizon,dan1/horizon-x509,anthonydillon/horizon,davidcusatis/horizon,saydulk/horizon,gerrive/horizon,bigswitch/horizon,django-leonardo/horizon,yeming233/horizon,vladryk/horizon,noironetworks/horizon,anthonydillon/horizon,idjaw/horizon,redhat-cip/horizon,gerrive/horizon,endorphinl/horizon-fork,ChameleonCloud/horizon,wolverineav/horizon,NeCTAR-RC/horizon,sandvine/horizon,endorphinl/horizon-fork,FNST-OpenStack/horizon,openstack/horizon,davidcusatis/horizon,saydulk/horizon,FNST-OpenStack/horizon,vladryk/horizon,Dark-Hacker/horizon,BiznetGIO/horizon,bac/horizon,Mirantis/mos-horizon,noironetworks/horizon,ChameleonCloud/horizon,anthonydillon/horizon,takeshineshiro/horizon,tqtran7/horizon,philoniare/horizon,bac/horizon,redhat-openstack/horizon,coreycb/horizon,bigswitch/horizon,yeming233/horizon,gerrive/horizon,yeming233/horizon,openstack/horizon,Dark-Hacker/horizon,Dark-Hacker/horizon