Clean up Horizon Apache configuration files in clean.sh

The horizon cleanup function wasn't being called at all during
cleanup which left the Apache configuration.

Change-Id: Iff5336d0c5e79cfc82f1c648afaabb869d86020e
diff --git a/clean.sh b/clean.sh
index 0641bff..452df02 100755
--- a/clean.sh
+++ b/clean.sh
@@ -95,6 +95,7 @@
 cleanup_nova
 cleanup_neutron
 cleanup_swift
+cleanup_horizon
 
 if is_service_enabled ldap; then
     cleanup_ldap
diff --git a/lib/horizon b/lib/horizon
index 0517e32..78cbe8b 100644
--- a/lib/horizon
+++ b/lib/horizon
@@ -69,9 +69,8 @@
 # cleanup_horizon() - Remove residual data files, anything left over from previous
 # runs that a clean run would need to clean up
 function cleanup_horizon {
-    local horizon_conf
-    horizon_conf=$(apache_site_config_for horizon)
-    sudo rm -f $horizon_conf
+    disable_apache_site horizon
+    sudo rm -f $(apache_site_config_for horizon)
 }
 
 # configure_horizon() - Set config files, create data dirs, etc