Fix home button in 500 page
Fix home button in 500 page

Currently, 500 page uses WEBROOT to set home link where WEBROOT is being taken
from horizon.conf module. However, this module sets only HORIZON_CONFIG.
As a result, 500 page is rendered with empty link, pointing home button
to current page.

This patch loads WEBROOT to horizon.conf, so it can be used in template
for 500 error page.

Change-Id: Icdd23703527a09a61d1326992b25a1004713444e
Closes-Bug: 1507563

redhat-cip/horizon,Tesora/tesora-horizon,BiznetGIO/horizon,gerrive/horizon,ChameleonCloud/horizon,yeming233/horizon,gerrive/horizon,redhat-cip/horizon,django-leonardo/horizon,Tesora/tesora-horizon,wolverineav/horizon,bigswitch/horizon,redhat-openstack/horizon,redhat-cip/horizon,gerrive/horizon,bac/horizon,sandvine/horizon,dan1/horizon-x509,davidcusatis/horizon,BiznetGIO/horizon,davidcusatis/horizon,bigswitch/horizon,noironetworks/horizon,gerrive/horizon,Tesora/tesora-horizon,Mirantis/mos-horizon,sandvine/horizon,Mirantis/mos-horizon,wolverineav/horizon,dan1/horizon-x509,ChameleonCloud/horizon,bigswitch/horizon,openstack/horizon,coreycb/horizon,dan1/horizon-x509,ChameleonCloud/horizon,bigswitch/horizon,BiznetGIO/horizon,NeCTAR-RC/horizon,coreycb/horizon,sandvine/horizon,openstack/horizon,NeCTAR-RC/horizon,dan1/horizon-x509,BiznetGIO/horizon,noironetworks/horizon,wolverineav/horizon,openstack/horizon,bac/horizon,coreycb/horizon,Mirantis/mos-horizon,redhat-openstack/horizon,yeming233/horizon,Tesora/tesora-horizon,coreycb/horizon,django-leonardo/horizon,django-leonardo/horizon,bac/horizon,sandvine/horizon,openstack/horizon,redhat-openstack/horizon,davidcusatis/horizon,NeCTAR-RC/horizon,noironetworks/horizon,redhat-cip/horizon,django-leonardo/horizon,redhat-openstack/horizon,wolverineav/horizon,Mirantis/mos-horizon,yeming233/horizon,noironetworks/horizon,bac/horizon,yeming233/horizon,davidcusatis/horizon,NeCTAR-RC/horizon,ChameleonCloud/horizon