Use example settings in horizon repo as local_settings.py

The current horizon_settings.py in devstack is out-of-date and we
tend to forget to update this file. This commit changes devstack
to use the example settings in horizon repo.

Change-Id: I0bb6af21a806a72ed59f31b094dd21da85ca335e
diff --git a/lib/horizon b/lib/horizon
index 9c96b58..bc739ed 100644
--- a/lib/horizon
+++ b/lib/horizon
@@ -29,6 +29,10 @@
 # Set up default directories
 HORIZON_DIR=$DEST/horizon
 
+# local_settings.py is used to customize Dashboard settings.
+# The example file in Horizon repo is used by default.
+HORIZON_SETTINGS=${HORIZON_SETTINGS:-$HORIZON_DIR/openstack_dashboard/local/local_settings.py.example}
+
 # Allow overriding the default Apache user and group, default to
 # current user and his default group.
 APACHE_USER=${APACHE_USER:-$USER}
@@ -77,7 +81,7 @@
 
     # ``local_settings.py`` is used to override horizon default settings.
     local_settings=$HORIZON_DIR/openstack_dashboard/local/local_settings.py
-    cp $FILES/horizon_settings.py $local_settings
+    cp $HORIZON_SETTINGS $local_settings
 
     # enable loadbalancer dashboard in case service is enabled
     if is_service_enabled q-lbaas; then